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Methodology and sources
Every number behind Lull's calculators, one row each, with where it comes from and when we last read the source. The tool results link here so you can check any figure yourself.
How to read this page
Every number the calculators use is one row below, with its unit, its source, the year of that source, a tier, the date we last read the source page and the tools that use it. Each row has its own link, and the results on the tool pages link straight to the rows behind them. The data file holds 129 values from 50 sources (a source counts when it backs at least one value):
- Primary 106 values read straight off the source page: 101 with the words we read quoted, and 5 from USDA food records, where the row names the record's caffeine and serving figures.
- Secondary 1 value reported by the source from another body, with that body named.
- Studio rule 22 values we chose because no source gives one, each with the reason. 5 of them are sanity limits or gaps of our own that lean on no source, and say so; the rest name the source they lean on.
The same file feeds the calculators and the text of every tool page. A check in our build fails if a page shows a number that is not from this file, a worked result from it, or an input you can change, so the pages and this table cannot drift apart. The sources are re-read every quarter and when a value is added; changes are dated in the changelog.
Every value, by tool
Rows used by more than one tool appear once, under the first tool that uses it.
Sleep calculator
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Sleep cycle length, low end of the published range 80 min | Primary | NIH/NHLBI, 2022The cycle starts over every 80 to 100 minutes. | Sleep calculator, Nap planner | |
| Sleep cycle length, high end of the published range 100 min | Primary | NIH/NHLBI, 2022The cycle starts over every 80 to 100 minutes. | Sleep calculator, Nap planner | |
| Cycles in a night, usual low 4 cycles | Primary | NIH/NHLBI, 2022Usually there are four to six cycles per night. | Sleep calculator | |
| Cycles in a night, usual high 6 cycles | Primary | NIH/NHLBI, 2022Usually there are four to six cycles per night. | Sleep calculator | |
| First REM sleep after falling asleep 90 min | Primary | NIH/NINDS, 2025REM sleep first occurs about 90 minutes after falling asleep. | Sleep calculator | |
| Cycle length the calculator counts in 90 min | Studio rule | Our rule, leaning on NIH/NHLBI, 2022 Our choice: a flat figure inside the NHLBI range that matches the NINDS first-REM timing. Real cycles vary between people and nights. | Sleep calculator, Guide: Dark winter mornings, Guide: Sleeping on a plane | |
| Time allowed to fall asleep 15 min | Studio rule | Our rule, leaning on CDC/NIOSH, 2020 Our allowance, inside the up-to-about-25-minutes NIOSH describes as normal sleep onset. | Sleep calculator, Sleep need by age, Night-shift sleep planner, Nap planner, Sleep debt calculator, Guide: 12-hour night shift schedules, Guide: Dark winter mornings, Guide: Clock-change sleep plan, Guide: School-night bedtimes, Guide: Kids' bedtime routine, Guide: One-hour wind-down | |
| Normal sleep onset, upper figure 25 min | Primary | CDC/NIOSH, 2020Normal sleep onset takes up to about 25 minutes. | Sleep calculator | |
| Time to fall asleep that NIOSH lists as a symptom to raise with a health care provider 30 min | Primary | CDC/NIOSH, 2020It takes you more than 30 minutes to fall asleep at night. | Sleep calculator, Sleep need by age, Night-shift sleep planner, Nap planner, Sleep debt calculator, Social jet lag calculator, Guide: 12-hour night shift schedules, Guide: Dark winter mornings, Guide: Clock-change sleep plan, Guide: Weekend catch-up sleep, Guide: One-hour wind-down, Guide: How long caffeine stays | |
| US (CDC): recommended sleep, school age 6 to 12 years: 9 to 12 hours a day | Primary | CDC, 2024School age 6–12 years 9–12 hours | Sleep calculator, Sleep need by age, Sleep debt calculator, Guide: School-night bedtimes | |
| US (CDC): recommended sleep, teen 13 to 17 years: 8 to 10 hours a day | Primary | CDC, 2024Teen 13–17 years 8–10 hours | Sleep calculator, Sleep need by age, Sleep debt calculator, Guide: School-night bedtimes | |
| US (CDC): recommended sleep, adult 18 to 60 years: 7 or more hours a day | Primary | CDC, 2024Adult 18–60 years 7 or more hours | Sleep calculator, Sleep need by age, Night-shift sleep planner, Sleep debt calculator, Guide: 12-hour night shift schedules, Guide: Dark winter mornings, Guide: Clock-change sleep plan, Guide: Weekend catch-up sleep | |
| US (CDC): recommended sleep, adult 61 to 64 years: 7 to 9 hours a day | Primary | CDC, 2024Adult 61–64 years 7–9 hours | Sleep calculator, Sleep need by age, Sleep debt calculator | |
| US (CDC): recommended sleep, older adult 65 years and over: 7 to 8 hours a day | Primary | CDC, 2024Adult 65 years and older 7–8 hours | Sleep calculator, Sleep need by age, Sleep debt calculator | |
| Options shown around the suggested cycle count 1 fewer and up to 2 more than the suggestion | Studio rule | Our rule, leaning on CDC, 2024 The suggestion is the fewest whole cycles that give more than the bottom of the CDC range for the age group; the cards add one fewer and up to two more. | Sleep calculator | |
| Nap that ends at the end of a sleep cycle 90 min | Primary | CDC/NIOSH, 2020If you wake up from a nap in either 20 minutes (before going into deeper sleep) or about 90 minutes (predicted to be the end of a sleep cycle), grogginess from sleep inertia may be less on awakening | Sleep calculator, Night-shift sleep planner, Nap planner, Guide: 12-hour night shift schedules | |
| Keep light low before bed 1 to 2 h before bedtime | Primary | CDC/NIOSH, 2020Keep light levels low 1-2 hours before bedtime. | Sleep calculator, Jet lag planner, Guide: Dark winter mornings, Guide: One-hour wind-down | |
| Electronic devices off before bed (CDC) 30 min before bedtime | Primary | CDC, 2024Turning off electronic devices at least 30 minutes before bedtime. | Sleep calculator, Guide: One-hour wind-down |
Sleep need by age
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| US (CDC): recommended sleep, newborn 0 to 3 months: 14 to 17 hours a day | Primary | CDC, 2024Newborn 0–3 months 14–17 hours | Sleep need by age | |
| US (CDC): recommended sleep, infant 4 to 12 months: 12 to 16 hours a day, including naps | Primary | CDC, 2024Infant 4–12 months 12–16 hours (including naps) | Sleep need by age | |
| US (CDC): recommended sleep, toddler 1 to 2 years: 11 to 14 hours a day, including naps | Primary | CDC, 2024Toddler 1–2 years 11–14 hours (including naps) | Sleep need by age | |
| US (CDC): recommended sleep, preschool 3 to 5 years: 10 to 13 hours a day, including naps | Primary | CDC, 2024Preschool 3–5 years 10–13 hours (including naps) | Sleep need by age, Guide: School-night bedtimes | |
| UK (NHS): adults 18 years and over: 7 to 9 hours a night | Primary | NHS (UK), 2024adults need 7 to 9 hours The NHS does not give an age for 'adults'; we read it as 18 and over. | Sleep need by age | |
| UK (NHS): children, no ages given 9 to 13 hours a night | Primary | NHS (UK), 2024children need 9 to 13 hours The NHS gives no age band for this figure, so the tool shows it as a note, not as the UK range for an age. | Sleep need by age, Guide: School-night bedtimes | |
| UK (NHS): toddlers and babies, no ages given 12 to 17 hours a night | Primary | NHS (UK), 2024toddlers and babies need 12 to 17 hours The NHS gives no age band for this figure, so the tool shows it as a note, not as the UK range for an age. | Sleep need by age | |
| Canada: infants, younger 0 to 3 months: 14 to 17 hours a day, including naps | Primary | Canada: Canadian 24-Hour Movement Guidelines (CSEP), 201714 to 17 hours (for those aged 0-3 months) | Sleep need by age | |
| Canada: infants, older 4 to 11 months: 12 to 16 hours a day, including naps | Primary | Canada: Canadian 24-Hour Movement Guidelines (CSEP), 201712 to 16 hours (for those aged 4-11 months) of good-quality sleep, including naps | Sleep need by age | |
| Canada: toddlers 1 to 2 years: 11 to 14 hours a day, including naps | Primary | Canada: Canadian 24-Hour Movement Guidelines (CSEP), 201711 to 14 hours of good-quality sleep, including naps | Sleep need by age | |
| Canada: preschoolers 3 to 4 years: 10 to 13 hours a day, including naps | Primary | Canada: Canadian 24-Hour Movement Guidelines (CSEP), 201710 to 13 hours of good-quality sleep, which may include a nap | Sleep need by age | |
| Canada: children 5 to 13 years: 9 to 11 hours a night | Primary | Canada: Public Health Agency of Canada, 20269 to 11 hours of sleep per night for children ages 5 to 13 years | Sleep need by age, Guide: School-night bedtimes | |
| Canada: youth 14 to 17 years: 8 to 10 hours a night | Primary | Canada: Public Health Agency of Canada, 20268 to 10 hours of sleep per night for youth ages 14 to 17 years | Sleep need by age, Guide: School-night bedtimes | |
| Canada: adults 18 to 64 years: 7 to 9 hours a night | Primary | Canada: Public Health Agency of Canada, 20267 to 9 hours of sleep for adults 18 to 64 years | Sleep need by age | |
| Canada: older adults 65 years and over: 7 to 8 hours a night | Primary | Canada: Public Health Agency of Canada, 20267 to 8 hours of sleep for adults 65 years and older | Sleep need by age | |
| Australia: babies, younger 0 to 3 months: 14 to 17 hours a day, including naps | Primary | Australia: Department of Health, Disability and Ageing, 202614 to 17 hours until 3 months | Sleep need by age | |
| Australia: babies, older 4 to 11 months: 12 to 16 hours a day, including naps | Primary | Australia: Department of Health, Disability and Ageing, 202612 to 16 hours from 4 to 11 months | Sleep need by age | |
| Australia: toddlers 1 to 2 years: 11 to 14 hours a day, including naps | Primary | Australia: Department of Health, Disability and Ageing, 2026Toddlers need 11 to 14 hours of good quality sleep every day, including naps | Sleep need by age | |
| Australia: preschoolers 3 to 5 years: 10 to 13 hours a day | Primary | Australia: Department of Health, Disability and Ageing, 2026Preschoolers need 10 to 13 hours of good quality sleep every day Australia's preschool band (3 to 5) and children's band (5 to 13) both include age 5; the tool uses the children's band from 5. | Sleep need by age | |
| Australia: children 5 to 13 years: 9 to 11 hours a night | Primary | Australia: Department of Health, Disability and Ageing, 2026children aged 5 to 13 years get 9 to 11 hours of uninterrupted sleep | Sleep need by age | |
| Australia: young people 14 to 17 years: 8 to 10 hours a night | Primary | Australia: Department of Health, Disability and Ageing, 2026young people aged 14 to 17 years get 8 to 10 hours of uninterrupted sleep | Sleep need by age | |
| Australia: adults 18 to 64 years: 7 to 9 hours a night | Primary | Australia: Department of Health, Disability and Ageing, 2026Sleep 7-9 hours of good quality sleep with consistent bed and wake up times. | Sleep need by age | |
| Australia: older adults 65 years and over: 7 to 8 hours a night | Primary | Australia: Department of Health, Disability and Ageing, 2026Sleep 7-8 hours of good quality sleep with consistent bed and wake up times. | Sleep need by age |
Night-shift sleep planner
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Short nap that ends before deeper sleep 20 min | Primary | CDC/NIOSH, 2020If you wake up from a nap in either 20 minutes (before going into deeper sleep) or about 90 minutes (predicted to be the end of a sleep cycle), grogginess from sleep inertia may be less on awakening | Night-shift sleep planner, Nap planner, Guide: 12-hour night shift schedules | |
| Shortest pre-night-shift nap in the studies NIOSH lists 1.5 h | Primary | CDC/NIOSH, 2020Nurses and nursing aides who took a 1.5-hour nap (3:30 to 5:00 p.m.) perceived significantly more alertness | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Longest pre-night-shift nap in the studies NIOSH lists 3 h | Primary | CDC/NIOSH, 2020Taking a 3-hour nap (2 to 5 p.m.) produced higher alertness during a subsequent night shift | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Caffeine half-life, low figure 5 h | Primary | CDC/NIOSH, 2020has a half-life of 5 to 6 hours but can remain in your system much longer | Night-shift sleep planner, Caffeine cut-off calculator, Guide: 12-hour night shift schedules, Guide: How long caffeine stays | |
| Caffeine half-life, high figure 6 h | Primary | CDC/NIOSH, 2020has a half-life of 5 to 6 hours but can remain in your system much longer | Night-shift sleep planner, Caffeine cut-off calculator, Guide: 12-hour night shift schedules, Guide: How long caffeine stays | |
| Last caffeine before daytime sleep 6 h before sleep | Studio rule | Our rule, leaning on CDC/NIOSH, 2020 Our rule: one half-life at the top of the NIOSH range before you lie down. NIOSH itself says to stop several hours before the shift ends, without a number. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Daytime sleep is better taken before this clock time 2:00 PM | Primary | CDC/NIOSH, 2020The more sleep you get before 2 p.m., the better rested you will be. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Brighter light in the first half of the shift, less in the second the first half of the shift | Primary | CDC/NIOSH, 2020You can be more alert if you increase your light exposure during the first half of the shift. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Night shift length NIOSH says is better tolerated (or less) 8 h | Primary | CDC/NIOSH, 2020During the evening and night, shorter shifts (8 hours or less) are better tolerated than longer shifts. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Work-hours limit in any 24 hours recommended for nurses by the Institute of Medicine 12 h | Secondary | CDC/NIOSH, 2020 Institute of Medicine report Keeping Patients Safe (2004), as reported by NIOSH. We use it as the point where the planner adds a drowsy-driving note. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Time between a pre-shift nap alarm and leaving for work 45 min | Studio rule | Our rule, leaning on CDC/NIOSH, 2020 Our allowance to wake up, get ready and let grogginess pass before the trip. | Night-shift sleep planner, Guide: 12-hour night shift schedules | |
| Least time awake between daytime sleep and a pre-shift nap 60 min | Studio rule | Our rule; no source gives this figure Our rule: below this the nap is folded into the main sleep and not offered. | Night-shift sleep planner | |
| Shortest shift the planner accepts 4 h | Studio rule | Our rule; no source gives this figure Sanity limit: shorter entries are read as a typo. | Night-shift sleep planner | |
| Longest shift the planner accepts 14 h | Studio rule | Our rule; no source gives this figure Sanity limit: longer entries are read as a typo. | Night-shift sleep planner | |
| A shift counts as a night shift when at least this much of it falls between these times at least 3 h between 10:00 PM and 6:00 AM | Studio rule | Our rule, leaning on CDC/NIOSH, 2016 Our test (3 hours between 10 PM and 6 AM). NIOSH's survey used a wider band (any hours between 7 p.m. and 8 a.m.), which would also take in evening shifts. | Night-shift sleep planner |
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Nap planner
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Short daytime naps the Yellow Book describes for travellers 20 to 30 min | Primary | CDC Yellow Book, 2025Short daytime naps (20–30 minutes) can be utilized to help sustain alertness during the local day | Nap planner, Jet lag planner, Guide: Jet lag east vs west, Guide: Sleeping on a plane | |
| Nap length that did best in Brooks and Lack's small study 10 min | Primary | Brooks and Lack, Sleep, 2006the 10-minute nap was overall the most effective afternoon nap duration of the nap lengths examined in this study | Nap planner | |
| Least sleep the nap planner will plan 10 min of sleep | Studio rule | Our rule, leaning on Brooks and Lack, Sleep, 2006 Our floor: with less room than this after falling asleep, the planner says there is not enough time. It matches the shortest nap that helped quickly in Brooks and Lack's study. | Nap planner | |
| No-nap window before bedtime (choices, default in the middle) 4, 6 (the default) or 8 h before bedtime | Studio rule | Our rule, leaning on CDC/NIOSH, 2020 Our rule of thumb, not a published figure. The planner checks it against when the nap ends. | Nap planner | |
| Hours awake before a nap that the planner flags for a check 16 h awake | Studio rule | Our rule; no source gives this figure A sanity check on the times entered, not a health limit. | Nap planner | |
| How long sleep inertia typically lasts 30 to 60 min | Primary | CDC/NIOSH, 2020Research indicates this typically can last from 30 to 60 minutes, but researchers have observed it lasting 2 hours | Nap planner | |
| Longest sleep inertia researchers have observed, as NIOSH reports it 2 h | Primary | CDC/NIOSH, 2020Research indicates this typically can last from 30 to 60 minutes, but researchers have observed it lasting 2 hours | Nap planner | |
| Grogginess after a 20 or about 90 minute nap may clear within 15 to 30 min | Primary | CDC/NIOSH, 2020If you wake up from a nap in either 20 minutes (before going into deeper sleep) or about 90 minutes (predicted to be the end of a sleep cycle), grogginess from sleep inertia may be less on awakening and may go away more quickly (within 15 to 30 minutes) | Nap planner | |
| Time caffeine takes to reach full effect 30 min | Primary | CDC/NIOSH, 2020Caffeine takes about 30 minutes to reach full effect | Nap planner |
Jet lag planner
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Average adjustment when the body clock moves earlier (eastward) 1 h a day | Primary | CDC Yellow Book, 2025an average rate of adaptation of 1.5 hrs/day for westward travel and 1 hr/day for eastward travel | Jet lag planner, Guide: Jet lag east vs west, Guide: Sleeping on a plane | |
| Average adjustment when the body clock moves later (westward) 1.5 h a day | Primary | CDC Yellow Book, 2025an average rate of adaptation of 1.5 hrs/day for westward travel and 1 hr/day for eastward travel | Jet lag planner, Guide: Jet lag east vs west | |
| Shifting sleep before the trip 1 h a day for 2 to 3 days before the trip | Primary | CDC Yellow Book, 2025shifting sleep 1 hour later (for westward travel) or earlier (for eastward travel) per day in the 2–3 days prior to the trip may reduce the amount of time required to adjust | Jet lag planner, Guide: Jet lag east vs west, Guide: Sleeping on a plane | |
| Body clock low point (circadian nadir) 2 to 4 h before your usual wake time | Primary | CDC Yellow Book, 2025the circadian nadir (approximately 2–4 hours prior to habitual wake time) | Jet lag planner, Social jet lag calculator, Guide: Jet lag east vs west, Guide: Dark winter mornings | |
| Light windows in the jet lag plan moving earlier: bright light for 3 h after waking, low light for 2 h before bed; moving later: bright light from 4 h to 1 h before bed, low light for 2 h after waking | Studio rule | Our rule, leaning on CDC Yellow Book, 2025 Our windows built on the Yellow Book principle that morning light moves the clock earlier and evening light later. Moving earlier: bright light for 3 hours after waking, low light for 2 hours before bed (the top of NIOSH's 1 to 2 hours). Moving later: bright light from 4 hours to 1 hour before bed, low light for 2 hours after waking. | Jet lag planner | |
| Bedtimes outside this window are flagged as hard to keep from 8:00 PM to 3:00 AM | Studio rule | Our rule, leaning on CDC Yellow Book, 2025 Our flag (8 PM to 3 AM). Outside it, the planned bedtime is a target that may be hard to keep. | Jet lag planner | |
| Clock shift from which the plan marks its light times as approximate 6 h | Studio rule | Our rule, leaning on CDC Yellow Book, 2025 Our cut-off. The Yellow Book says the best light timing depends on the direction and the number of time zones crossed, without a simple rule we could turn into clock times for long trips. | Jet lag planner |
Caffeine cut-off calculator
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Brewed coffee 40 mg per 100 g; 1 cup (8 fl oz) = 237 g, so about 95 mg | Primary | USDA FoodData Central, 2019 Caffeine per 100 g and the gram weight of the portion, both read off the USDA record. The tool multiplies them. | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Espresso 212 mg per 100 g; 1 fl oz shot = 29.6 g, so about 63 mg | Primary | USDA FoodData Central, 2019 Caffeine per 100 g and the gram weight of the portion, both read off the USDA record. The tool multiplies them. | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Black tea 20 mg per 100 g; 1 cup (8 fl oz) = 237 g, so about 47 mg | Primary | USDA FoodData Central, 2019 Caffeine per 100 g and the gram weight of the portion, both read off the USDA record. The tool multiplies them. | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Cola 9 mg per 100 g; 12 fl oz can = 370 g, so about 33 mg | Primary | USDA FoodData Central, 2019 Caffeine per 100 g and the gram weight of the portion, both read off the USDA record. The tool multiplies them. | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Energy drink 29 mg per 100 g; 8.4 fl oz can = 258 g, so about 75 mg | Primary | USDA FoodData Central, 2019 Caffeine per 100 g and the gram weight of the portion, both read off the USDA record for one branded energy drink. Other brands differ a lot (see the FDA range). | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Default caffeine amount still active at bedtime 50 mg at bedtime | Studio rule | Our rule, leaning on US FDA, 2024 Our starting figure, which you can change. No official body gives an amount of caffeine that is fine at bedtime. | Caffeine cut-off calculator, Guide: Dark winter mornings, Guide: One-hour wind-down, Guide: How long caffeine stays | |
| Daily amount the FDA cites as not generally associated with negative effects for most adults 400 mg a day | Primary | US FDA, 2024For most adults, the FDA has cited 400 milligrams a day | Caffeine cut-off calculator, Guide: 12-hour night shift schedules, Guide: How long caffeine stays | |
| Caffeine in decaf coffee 2 to 15 mg per 8 fl oz cup | Primary | US FDA, 2024decaf coffee typically has 2 to 15 milligrams in an 8-fluid-ounce cup | Caffeine cut-off calculator | |
| Caffeine in energy drinks, range across brands 54 to 328 mg per 16 fl oz | Primary | US FDA, 2024energy drinks have 54 to 328 milligrams of caffeine per 16 fluid ounces | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Caffeine amount in the Drake 2013 study 400 mg | Primary | Drake et al., J Clin Sleep Med, 2013caffeine (400 mg) administered at 0, 3, and 6 hours prior to habitual bedtime | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Earliest time before bed in the Drake 2013 study that still disturbed sleep 6 h before bedtime | Primary | Drake et al., J Clin Sleep Med, 2013caffeine taken 6 hours before bedtime has important disruptive effects on sleep | Caffeine cut-off calculator, Guide: How long caffeine stays | |
| Latest cut-off the caffeine calculator shows 6 h before bedtime | Studio rule | Our rule, leaning on Drake et al., J Clin Sleep Med, 2013 Our rule: when the half-life gives a clock time, the calculator shows the earlier of that time and this mark, and says which one set it. A drink already at or under your bedtime figure shows any time. In Drake and colleagues' study, 400 mg of caffeine taken 6 hours before bedtime still disturbed sleep; the study did not test smaller amounts. | Caffeine cut-off calculator, Guide: One-hour wind-down, Guide: How long caffeine stays |
Sleep debt calculator
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| NIOSH's worked sleep debt example 8 h need, 6 h slept a day for 5 days: 10 h short | Primary | CDC/NIOSH, 2020A person with an 8-hour sleep need who gets 6 hours of sleep each day for 5 days accumulates a sleep debt of 10 hours. | Sleep debt calculator |
Social jet lag calculator
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Bands for the gap between free-day and workday mid-sleep low under 1 h, middle 1 h to 2 h, high over 2 h; check the times from 6 h | Studio rule | Our rule, leaning on Roenneberg et al., Current Biology, 2012 Our bands: under 1 hour, 1 to 2 hours, over 2 hours. From 6 hours the tool asks you to check the times. The gap itself is the published measure (free-day minus workday mid-sleep); no official body gives cut-offs. | Social jet lag calculator |
Guide: Clock-change sleep plan
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| US: clocks go forward the second Sunday in March, 2:00 AM local time | Primary | NIST, 2026begins at 2:00 a.m. on the second Sunday of March | Guide: Clock-change sleep plan | |
| US: clocks go back the first Sunday in November, 2:00 AM local time | Primary | NIST, 2026ends at 2:00 a.m. on the first Sunday of November | Guide: Clock-change sleep plan, Guide: Dark winter mornings | |
| EU: summer time begins the last Sunday in March, 1:00 AM GMT | Primary | European Union (EUR-Lex), 2001the summer-time period shall begin, in every Member State, at 1.00 a.m., Greenwich Mean Time, on the last Sunday in March | Guide: Clock-change sleep plan | |
| EU: summer time ends the last Sunday in October, 1:00 AM GMT | Primary | European Union (EUR-Lex), 2001the summer-time period shall end, in every Member State, at 1.00 a.m., Greenwich Mean Time, on the last Sunday in October | Guide: Clock-change sleep plan | |
| UK: clocks go forward the last Sunday in March, 1:00 AM local time | Primary | GOV.UK, 2026In the UK the clocks go forward 1 hour at 1am on the last Sunday in March, and back 1 hour at 2am on the last Sunday in October. | Guide: Clock-change sleep plan | |
| UK: clocks go back the last Sunday in October, 2:00 AM local time | Primary | GOV.UK, 2026In the UK the clocks go forward 1 hour at 1am on the last Sunday in March, and back 1 hour at 2am on the last Sunday in October. | Guide: Clock-change sleep plan | |
| Canada (Ontario's Time Act): clocks go forward the second Sunday in March, 2:00 AM local time | Primary | Government of Ontario, 1990daylight saving time during the period between 2 a.m. standard time on the second Sunday in March and 2 a.m. daylight saving time on the first Sunday in November | Guide: Clock-change sleep plan | |
| Canada (Ontario's Time Act): clocks go back the first Sunday in November, 2:00 AM local time | Primary | Government of Ontario, 1990daylight saving time during the period between 2 a.m. standard time on the second Sunday in March and 2 a.m. daylight saving time on the first Sunday in November | Guide: Clock-change sleep plan | |
| Australia (Victoria, NSW, ACT, SA, Tasmania): daylight saving begins the first Sunday in October, 2:00 AM local time | Primary | Business Victoria (Victorian Government), 2026Daylight Saving Time begins at 2am on the first Sunday in October when clocks are put forward one hour. | Guide: Clock-change sleep plan | |
| Australia (Victoria, NSW, ACT, SA, Tasmania): daylight saving ends the first Sunday in April, 3:00 AM local time | Primary | Business Victoria (Victorian Government), 2026Daylight Saving Time ends at 2am (3am Daylight Saving Time) on the first Sunday in April when clocks are put back one hour. | Guide: Clock-change sleep plan | |
| How far the clocks move at each change 1 h | Primary | GOV.UK, 2026In the UK the clocks go forward 1 hour at 1am on the last Sunday in March, and back 1 hour at 2am on the last Sunday in October. | Guide: Clock-change sleep plan | |
| Bedtime step on the nights before a clock change 15 min a night | Primary | NSW Government, 2026adjust your bedtime by 15 minutes each night before the change | Guide: Clock-change sleep plan | |
| Start shifting sleep and wake times 2 to 3 days before the change | Primary | American Academy of Sleep Medicine, 2016Graduated adjustment of sleep and wake times beginning 2-3 days before DST can also help with this transition. | Guide: Clock-change sleep plan | |
| How long the clock change disturbs sleep 5 to 7 days | Primary | American Academy of Sleep Medicine, 2016Moving into or out of DST has adverse effects on sleep/wake patterns that last about 5-7 days | Guide: Clock-change sleep plan | |
| Sleep the AASM advises adults to get around a clock change 7 h a night | Primary | American Academy of Sleep Medicine, 2016adults obtain at least 7 hours of sleep per night preceding and following DST changes | Guide: Clock-change sleep plan |
Guide: Dark winter mornings
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Atmospheric refraction assumed at sunrise 0.83 degrees | Primary | NOAA Global Monitoring Laboratory, 2026For sunrise and sunset calculations, we assume 0.833° of atmospheric refraction. | Guide: Dark winter mornings | |
| Accuracy NOAA gives for its sunrise equations (latitudes up to 72°) 1 min | Primary | NOAA Global Monitoring Laboratory, 2026The sunrise and sunset results are theoretically accurate to within a minute for locations between +/- 72° latitude | Guide: Dark winter mornings | |
| The eight cities in the sunrise table New York 40.71, -74.01; Chicago 41.88, -87.63; Toronto 43.65, -79.38; London 51.51, -0.13; Dublin 53.35, -6.26; Edinburgh 55.95, -3.19; Belgrade 44.79, 20.45; Sydney -33.87, 151.21 | Studio rule | Our rule, leaning on NOAA Global Monitoring Laboratory, 2026 Our choice of cities and their city-center points, rounded to two decimals. Local clock times use the IANA time zone database built into the browser and Node.js. Sunrise moves by about a minute across a large city. | Guide: Dark winter mornings | |
| The winter the sunrise table covers November 2026 to February 2027 | Studio rule | Our rule; no source gives this figure Our choice: the coming winter, the 1st and 15th of November to February. Re-run once a year; sunrise on a date moves by about a minute from year to year, but the clock-change dates move. | Guide: Dark winter mornings | |
| Daylight window in the winter-morning plan 60 min after the alarm | Studio rule | Our rule, leaning on CDC Yellow Book, 2025 Our window: get outdoor daylight within the first hour after the alarm. The Yellow Book says bright light in the morning, after the body clock's low point, moves the clock earlier; it gives no minute figure for everyday life. | Guide: Dark winter mornings |
Guide: 12-hour night shift schedules
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Bedtime on days off in NIOSH's compromise schedule for night nurses from 3:00 AM to 4:00 AM | Primary | CDC/NIOSH, 2020On days off, try to stay up until the middle of the night (3-4 a.m.), and sleep until noon or 1 p.m. | Guide: 12-hour night shift schedules | |
| Wake time on days off in NIOSH's compromise schedule for night nurses from 12:00 PM to 1:00 PM | Primary | CDC/NIOSH, 2020On days off, try to stay up until the middle of the night (3-4 a.m.), and sleep until noon or 1 p.m. | Guide: 12-hour night shift schedules |
Guide: Jet lag east vs west
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| A trip short enough that the NHS says you could keep home times 2 to 3 days | Primary | NHS, 2023If your trip is short (2 to 3 days), you could try not changing your eating and sleeping times to the new time zone | Guide: Jet lag east vs west, Guide: Sleeping on a plane | |
| The common estimate of days to adjust, per time zone crossed 1 day per time zone | Primary | American Academy of Sleep Medicine (Sleep Education), 2026It is estimated that it takes one day per time zone for your body clock to fully adjust to local time. | Guide: Jet lag east vs west |
Guide: Kids' bedtime routine
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Screens off before a child's bedtime (AAP) 60 min before bedtime | Primary | American Academy of Pediatrics (HealthyChildren.org), 2026To prevent sleep disruption, turn off all screens at least 60 minutes/1 hour before bedtime. | Guide: Kids' bedtime routine | |
| Longest bedtime routine for a school-aged child (AAP) 30 min | Primary | American Academy of Pediatrics (HealthyChildren.org), 2013Try to keep the bedtime routine to no longer than 30 minutes. | Guide: Kids' bedtime routine | |
| Reading aloud together (AAP Brush, Book, Bed) 15 min a day | Primary | American Academy of Pediatrics (HealthyChildren.org), 2024Spending some time, even just 15 minutes each day, to read aloud together will help improve your child's language development and social-emotional skills. | Guide: Kids' bedtime routine | |
| Time for each short step of the routine chart (tidy-up, wash and pajamas, teeth) 5 min per step | Studio rule | Our rule, leaning on American Academy of Pediatrics (HealthyChildren.org), 2013 Our split of the AAP's 30-minute routine: 5 minutes each for the tidy-up, washing and pajamas, and teeth, then the AAP's 15 minutes of reading. The AAP gives no minutes for the short steps. | Guide: Kids' bedtime routine |
Guide: Weekend catch-up sleep
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| Short nights in the weekend-recovery study (Depner 2019) 5 h sleep opportunity a night | Primary | Depner et al., Current Biology, 2019sleep restriction without weekend recovery sleep (SR; 5-h sleep opportunities, n = 14) | Guide: Weekend catch-up sleep | |
| Short workweek before the recovery weekend (Depner 2019) 5 days | Primary | Depner et al., Current Biology, 2019insufficient sleep for 5-day workweek, then 2 days of weekend recovery, then 2 nights of insufficient sleep | Guide: Weekend catch-up sleep | |
| Recovery weekend (Depner 2019) 2 days | Primary | Depner et al., Current Biology, 2019then 2 days of weekend recovery | Guide: Weekend catch-up sleep | |
| Extra sleep over the recovery weekend, above baseline (Depner 2019) 1.1 h | Primary | Depner et al., Current Biology, 2019During ad libitum weekend recovery sleep, participants cumulatively slept ∼1.1 h more than baseline | Guide: Weekend catch-up sleep | |
| People in each short-sleep group (Depner 2019) 14 people per group | Primary | Depner et al., Current Biology, 2019n = 14 | Guide: Weekend catch-up sleep | |
| The 6-hour condition (Van Dongen 2003) 6 h in bed a night | Primary | Van Dongen et al., Sleep, 20034 h, 6 h, or 8 h time in bed per night | Guide: Weekend catch-up sleep | |
| The 4-hour condition (Van Dongen 2003) 4 h in bed a night | Primary | Van Dongen et al., Sleep, 20034 h, 6 h, or 8 h time in bed per night | Guide: Weekend catch-up sleep | |
| Length of the sleep restriction (Van Dongen 2003) 14 days | Primary | Van Dongen et al., Sleep, 2003which were maintained for 14 consecutive days | Guide: Weekend catch-up sleep | |
| Deficit equivalent after 14 days at 6 h or less (Van Dongen 2003) 2 nights without sleep | Primary | Van Dongen et al., Sleep, 2003chronic restriction of sleep to 6 h or less per night produced cognitive performance deficits equivalent to up to 2 nights of total sleep deprivation | Guide: Weekend catch-up sleep | |
| People in the study (Van Dongen 2003) 48 adults | Primary | Van Dongen et al., Sleep, 2003A total of n = 48 healthy adults (ages 21-38) participated in the experiments. | Guide: Weekend catch-up sleep |
Guide: One-hour wind-down
| Value | Tier | Source | Last checked | Used by |
|---|---|---|---|---|
| No heavy, spicy meals before bed (NIOSH) 2 to 3 h before bedtime | Primary | CDC/NIOSH, 2020Heavy, spicy meals 2 to 3 hours before | Guide: One-hour wind-down | |
| Finish exercise before bed if falling asleep is hard (NIOSH) 3 h before bedtime | Primary | CDC/NIOSH, 2020if you have trouble falling asleep, try finishing exercise at least 3 hours before bedtime. | Guide: One-hour wind-down | |
| Wind-down reminder alarm (NIOSH) 1 h before bedtime | Primary | CDC/NIOSH, 2020You can set an alarm an hour or so before bedtime to remind yourself to start doing only relaxing activities to get your body ready for sleep. | Guide: One-hour wind-down | |
| Electronic devices off before bed (AASM) 30 min before bedtime | Primary | American Academy of Sleep Medicine (Sleep Education), 2026Turn off electronic devices at least 30 minutes before bedtime. | Guide: One-hour wind-down | |
| Get out of bed if not asleep after (AASM) 20 min | Primary | American Academy of Sleep Medicine (Sleep Education), 2026If you don’t fall asleep after 20 minutes, get out of bed. | Guide: One-hour wind-down |
Sleep cycles: what the sources say
Sleep is not one even state. The NIH/NHLBI describes it as a cycle through stages of lighter non-REM sleep, deeper non-REM sleep and REM sleep, the stage most linked with dreaming, and says the cycle starts over every 80 to 100 minutes, with usually 4 to 6 cycles a night. The NIH/NINDS adds that REM sleep first occurs about 90 minutes after falling asleep. Neither gives one cycle length for everybody, and cycles vary from person to person and night to night.
The sleep calculator counts in cycles of 90 minutes, a studio rule: it sits inside the NHLBI range and matches the NINDS first-REM timing. For naps, NIOSH's training for nurses says that waking at about 90 minutes, the predicted end of a cycle, may leave less grogginess because you are likely to wake from lighter sleep; the calculator applies that idea to a night's sleep as its planning method, not as a published rule for the night. It is a planning aid built on averages, not a measurement of your own cycles.
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All sources
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- American Academy of Pediatrics (HealthyChildren.org) — Bedtime Routines for School-Aged Children2013 · read on
- American Academy of Pediatrics (HealthyChildren.org) — Brush, Book, Bed: How to Structure Your Child's Nighttime Routine2024 · read on
- American Academy of Sleep Medicine — Daylight Saving Time Health Advisory2016 · read on
- American Academy of Sleep Medicine (Sleep Education) — Healthy Sleep Habits2026 · read on
- American Academy of Sleep Medicine (Sleep Education) — Jet lag2026 · read on
- Australia: Department of Health, Disability and Ageing — 24-hour movement guidelines: infants, toddlers and preschoolers (birth to 5 years)2026 · read on
- Australia: Department of Health, Disability and Ageing — 24-hour movement guidelines: children and young people (5 to 17 years)2026 · read on
- Australia: Department of Health, Disability and Ageing — 24-hour movement guidelines: adults (18 to 64 years)2026 · read on
- Australia: Department of Health, Disability and Ageing — 24-hour movement guidelines: older adults (65 years and over)2026 · read on
- Brooks and Lack, Sleep — A brief afternoon nap following nocturnal sleep restriction: which nap duration is most recuperative? (abstract, PubMed)2006 · read on
- Business Victoria (Victorian Government) — Daylight saving2026 · read on
- Canada: Canadian 24-Hour Movement Guidelines (CSEP) — Early Years (0-4 years)2017 · read on
- Canada: Public Health Agency of Canada — Physical Activity, Sedentary Behaviour and Sleep (PASS) Indicators: key findings2026 · read on
- CDC — About Sleep (recommended hours by age)2024 · read on
- CDC Yellow Book — Jet Lag Disorder (2026 edition)2025 · read on
- CDC/NIOSH — Training for Nurses on Shift Work and Long Work Hours, Module 8: Relaxation Techniques2020 · read on
- CDC/NIOSH — Training for Nurses, Module 6: Do You Have Symptoms of a Sleep Disorder?2020 · read on
- CDC/NIOSH — Training for Nurses, Module 6: Sleep Aids and Stimulants, Caffeine2020 · read on
- CDC/NIOSH — Training for Nurses, Module 6: Prepare for Sleep2020 · read on
- CDC/NIOSH — Training for Nurses, Module 7: Nap Duration2020 · read on
- CDC/NIOSH — Training for Nurses, Module 7: Napping Before Nights2020 · read on
- CDC/NIOSH — Training for Nurses, Module 9: Coping with the Night and Evening Shifts, Light2020 · read on
- CDC/NIOSH — Training for Nurses, Module 9: Coping with the Night and Evening Shifts, Sleep2020 · read on
- CDC/NIOSH — Training for Nurses, Module 5: Guidelines for Designing Work Schedules2020 · read on
- CDC/NIOSH — Training for Nurses, Module 5: Extended Shifts2020 · read on
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- CDC/NIOSH — Training for Nurses, Module 7: Sleep Inertia2020 · read on
- CDC/NIOSH — Training for Nurses, Module 2: Sleep Pressure (sleep debt)2020 · read on
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- Government of Saskatchewan — Saskatchewan Time System2026 · read on
- Mindell and Williamson, Sleep Med Rev — Benefits of a bedtime routine in young children: Sleep, development, and beyond (abstract, PubMed)2018 · read on
- NHS — Jet lag2023 · read on
- NHS (UK) — Insomnia: how much sleep you need2024 · read on
- NIH/NHLBI — How Sleep Works: Sleep Phases and Stages2022 · read on
- NIH/NINDS — Brain Basics: Understanding Sleep2025 · read on
- NIST — Daylight Saving Time Rules2026 · read on
- NOAA Global Monitoring Laboratory — Solar Calculation Details2026 · read on
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- Roenneberg et al., Current Biology — Social Jetlag and Obesity (full text)2012 · read on
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- USDA FoodData Central — Beverages, coffee, brewed, espresso, restaurant-prepared (SR Legacy 171891)2019 · read on
- USDA FoodData Central — Beverages, tea, black, brewed, prepared with tap water (SR Legacy 173227)2019 · read on
- USDA FoodData Central — Beverages, carbonated, cola, regular (SR Legacy 174852)2019 · read on
- USDA FoodData Central — Beverages, Energy drink, RED BULL (SR Legacy 173210)2019 · read on
- Van Dongen et al., Sleep — The cumulative cost of additional wakefulness (abstract, PubMed)2003 · read on
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