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Sleep debt calculator: how many hours short are you?
For anyone who has had a run of short nights and wants a number instead of a vague sense of being behind. Enter the hours you slept on your last nights to see the total shortfall against your need, night by night, counted the way NIOSH counts it.
Sleeping 6 hours a night against an 8-hour need for 5 days leaves you 10 hours short. That is NIOSH's own example, and the calculator gets the same answer. For an adult it starts from 7 hours, the bottom of the CDC range.
Sleep debt calculator
The need starts at the bottom of the CDC range for the age group. Change it if you know you need more.
More settings: how many nights, wake-up time
Hours slept, oldest night first
Leave a night blank if you do not know it; blank nights are skipped. Each box takes 0 to 16 hours.
Your last 7 nights against a 7 hour need
Why this total?
Can you catch up on sleep on weekends? What the numbers say →
There’s no perfect night, only a better-planned one.
The Lull app has the sleep calculator from our home page, plus 6 sleep sounds that stop a minute before your phone’s alarm.
See the Lull appSleep debt in three example weeks
Three weeks of sleep against the calculator's starting need for an adult, 7 hours, each counted the way the calculator counts yours.
| Week | Hours slept, night by night | Short nights | Sleep debt |
|---|---|---|---|
| Short weeknights, long weekend | 6, 6, 6, 6, 6, 8, 8 | 5 | 5 h |
| One bad night | 7, 7, 4, 7, 7, 7, 7 | 1 | 3 h |
| Slightly short every night | 6.5, 6.5, 6.5, 6.5, 6.5, 6.5, 6.5 | 7 | 3 h 30 min |
The long weekend nights do not cancel the short weeknights. Each night counts only by how much it falls short of the need.
What the tally leaves out
This is a tally of hours against one number, not a measure of how you feel or how well you slept. Your real need is not exactly the bottom of a published range, hours you remember are often a little off, and the tool cannot know why a night was short. NIOSH says lost sleep does not have to be paid back hour for hour, so the total is a size, not a bill. Counting only the short nights is our choice, explained below.
See a doctor if you sleep enough hours but still feel exhausted, snore loudly, stop breathing at night, or regularly take more than 30 minutes to fall asleep (NIOSH lists that among the symptoms to raise with a health care provider). For a child or teen, ask the child's doctor about ongoing trouble settling or loud snoring. This page is general information, not medical advice: read our disclaimer.
How the tally works
For each night, the calculator takes the hours you needed minus the hours you slept, and keeps the answer only when it is above zero. The total of those shortfalls is the sleep debt for the nights you entered. This is the same arithmetic NIOSH uses in its training for nurses: a person with an 8-hour need who gets 6 hours for 5 days builds a debt of 10 hours, and the calculator gives that example the same answer.
Long nights are not subtracted from short ones. That is our choice: NIOSH notes that the body sometimes sleeps more soundly to pay down a debt, so an extra hour on one night is not a clean refund of an hour lost on another. Counting only the shortfalls keeps the total honest about the short nights. The average shortfall spreads the total over the nights you entered, which is easier to compare from week to week.
Worked example: a mixed week
An adult starts from the bottom of the CDC range, 7 h or more, so the need is 7 hours. Over seven nights they slept 6, 6.5, 7, 8, 5, 7, 9 hours. The short nights add up to 3 h 30 min, an average of 30 min a night, on 3 of the 7 nights. The two long nights give 3 h more than the need, but netting them off would show only 30 min, which hides how short the other nights were. With an alarm at 7:00 AM, a full 7 hours plus 15 minutes to fall asleep means lying down by 11:45 PM.
Where the total comes from, night by night
The large figure is the total shortfall. The boxes give the average shortfall, the average slept and how many nights fell short. The list shows each night against your need, so you can see whether the debt comes from one bad night or a run of slightly short ones. If you add a wake-up time, the result gives the clock time that leaves room for your full need, with the time to fall asleep included.
The values behind this total
Each row is one value this tool uses, with its tier: Primary = read off the source page, Secondary = reported by the source from another body, Studio rule = our own choice, with the reason given on the methodology page. The links in the result above go to the same rows there.
| Value | Tier | Source |
|---|---|---|
| NIOSH's worked sleep debt example 8 h need, 6 h slept a day for 5 days: 10 h short | Primary | CDC/NIOSH, 2020 |
| US (CDC): recommended sleep, school age 6 to 12 years: 9 to 12 hours a day | Primary | CDC, 2024 |
| US (CDC): recommended sleep, teen 13 to 17 years: 8 to 10 hours a day | Primary | CDC, 2024 |
| US (CDC): recommended sleep, adult 18 to 60 years: 7 or more hours a day | Primary | CDC, 2024 |
| US (CDC): recommended sleep, adult 61 to 64 years: 7 to 9 hours a day | Primary | CDC, 2024 |
| US (CDC): recommended sleep, older adult 65 years and over: 7 to 8 hours a day | Primary | CDC, 2024 |
| Time allowed to fall asleep 15 min | Studio rule | Our rule, leaning on CDC/NIOSH, 2020 |
| Time to fall asleep that NIOSH lists as a symptom to raise with a health care provider 30 min | Primary | CDC/NIOSH, 2020 |
Quotes, notes and the date we last read each source are on the methodology and sources page.
What NIOSH says about sleep debt
NIOSH's training for nurses on shift work describes sleep debt as building over time when you do not get the sleep you need, and says that sleep is needed to pay it down. It adds two cautions that shape how this tool reports its number. First, CDC/NIOSH says “A person does not necessarily need to pay back hour for hour the lost sleep, since the body sometimes sleeps more soundly to pay down the debt.” Second, it warns that even when sleepiness returns to normal after a day or two of extra sleep, thinking and reaction speed can still be below their usual level. So the tool shows a total and leaves out any schedule for paying it back.
What one study found about long weekends
Depner and colleagues (2019, Current Biology) had volunteers sleep too little during a working week and then as long as they liked at the weekend. When the short nights came back after the weekend, the volunteers' body clock timing had moved later and the changes in evening eating and body weight seen during the short nights returned. It was a small lab study of healthy young adults, so it shows a direction rather than a rule for everyone, but it fits NIOSH's point that sleep is better kept regular than paid back in one go. The abstract is on PubMed.
Where the starting need comes from
The age group sets the starting need to the bottom of the CDC's range: 9–12 h for 6–12 years, 8–10 h for 13–17 years, 7 h or more for 18–60 years, 7–9 h for 61–64 years and 7–8 h from 65. The bottom is the least demanding reading of each range, so the debt it gives is a floor. If you know you need more, raise the box: with a need one hour higher, the example above would show 8 h 30 min instead. Other countries publish different ranges for some ages; the sleep need by age tool puts them side by side.
Sleep debt questions
How is sleep debt calculated here?
Each night's hours are taken from your need, and only the shortfalls are added up. NIOSH's own example, an 8-hour need and 6 hours slept for 5 days, gives 10 hours, and so does this calculator.
How many hours do I need?
The tool starts from the bottom of the CDC range for your age group, for adults 7 h or more. Your own need may be higher, so you can change the number.
Why don't long nights cancel short ones?
Because NIOSH says lost sleep is not repaid hour for hour. Netting long nights against short ones would make a run of short nights look smaller than it was, so the tool counts only the shortfalls.
Can I make up lost sleep at the weekend?
NIOSH says sleep debt needs sleep to pay it down, but not hour for hour, and that thinking can stay slower after a day or two of extra sleep. A small lab study (Depner and colleagues, 2019) found that long weekend sleep moved the body clock later. This tool does not give a schedule.
Is what I enter stored anywhere?
No. The total is worked out in your browser. The share link holds only your need, the nights and the wake-up time, and only if you copy it.
More questions about the site, its sources and privacy are answered in the Lull FAQ.