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About Lull
Lull is a set of eight sleep timing calculators at instacalc.co, run by Quiet Hours Studio from Serbia and paid for by advertising. If a figure looks wrong, email support@instacalc.co: we check it against its source and log every correction in the changelog.
Why Lull exists
Most of what's known about sleep is published and free to read. The NIH describes how sleep cycles run. The CDC sets out how much sleep each age group needs, NIOSH has guidance on naps and on sleeping after night work, and the FDA writes about caffeine. Very little of it reaches a tired person in the form they need at bedtime, which is a time on the clock.
Lull exists to do that last step. You tell it the time that's fixed, usually an alarm, and it works out the rest: when to go to bed, how long to nap, when to stop drinking coffee, how to shift your sleep before a long flight.
We don't think there's a perfect night to aim for. We think a better-planned one is worth having, and that the plan should start from the morning you've actually got.
Sleep advice should also be checkable. A tip with no source asks you to take it on trust, and tired people have been sold plenty of tips. So every figure on the site, 129 values from 50 sources, sits in one data file. Next to each is the page it comes from, that page's year and the date we last read it. The methodology page lists them all.
Where no source gives a figure, we chose one and labeled it a studio rule. The two you'll meet most are a 90-minute sleep cycle, which sits inside the NIH's range of 80 to 100 minutes, and 15 minutes to fall asleep. Our build stops if a page shows a number that doesn't come from that file.
The Lull app for Android has the same bedtime calculator, with age presets that adjust the cycle length, and 6 sleep sounds with a timer that can stop the sound a minute before your phone's alarm.
What we promise: public sources, read at the source; every value shown; our own rules marked as ours; corrections dated in the changelog. No guilt about the sleep you didn't get: a short night before an early start is simply tonight's plan. The site is free and carries ads, and no ad ever changes a time. The app is free too. It has one banner ad, and a one-time $1.99 removes it.
And the limits, plainly. Lull can't know your body clock, your health or how you slept last night. Cycles vary from person to person and from night to night, so every result is an estimate. None of it is medical advice. If you regularly take more than 30 minutes to fall asleep, feel sleepy through the day after a full night, or snore loudly with pauses in your breathing, see a doctor.
Who runs Lull
Lull is a Quiet Hours Studio project, run from Serbia. Quiet Hours Studio builds and maintains practical web tools and apps, including the Lull Android app. The name is a trading name, not a registered company. We are not a medical organisation, a clinic or a research institute, and we do not claim medical credentials. The guidance the calculators use comes from public health bodies and published studies. We cite them; we are not affiliated with any of them, and none of them has reviewed or endorsed this site.
How the site is paid for
Lull costs nothing to use and is paid for by advertising served by Google. Advertising never changes a number, a time or a recommendation. We take no paid placements and no sponsored content, we use no affiliate links, and we do not sell visitor data. The only products we link to are our own: the Lull Android app and CalcThat. Ads appear on the calculator pages, below the calculators and their results; there are none on this page, the app page, the editorial and testing pages, the contact page or the legal pages.
What is on the site
The sleep calculator, the sleep need by age tool, the night-shift sleep planner, the nap planner, the jet lag planner, the caffeine cut-off calculator, the sleep debt calculator and the social jet lag calculator. Each answers one question, and the tools page says which. Behind them sit the methodology and sources page, which lists every value the calculators use, and the changelog, which dates every change and correction.
How the numbers are made
Every figure the calculators use, 86 values from 33 sources, lives in one data file with its unit, the source page that shows it, the year of that source, the date we last read it and a tier. Of those, 67 are read straight off the source page, 1 is a figure the cited page reports from another body, which is named in the row, and 18 are studio rules: figures we chose because no source gives one, labelled as ours wherever they appear. The same file also holds the figures our sleep timing guides add, which brings it to 129 values from 50 sources. The calculators and the text of every tool page and guide are built from that file, and our build fails if a page shows a number that does not come from it.
How a figure gets onto the site, how often the sources are re-read and how corrections are handled is set out in our editorial and corrections policy. Every calculator is checked against cases worked out by hand on how we test.
What the calculators are not
They are planning aids that turn published averages and a few labelled rules of our own into clock times. They cannot know your own body clock, health or sleep, so every result is an estimate, not a measurement, and nothing on Lull is medical advice. Persistent trouble sleeping, heavy daytime sleepiness, loud snoring with pauses in breathing, or sleep problems affecting your mood are reasons to speak to a doctor. The full wording is in our disclaimer.
Your answers stay in your browser
The calculators run in your browser, with no account. What you type is not sent to us. A share link carries only the inputs of one tool, and only if you copy it. The privacy policy describes the analytics and advertising scripts the site uses.
Get in touch
Questions, feedback and corrections go to support@instacalc.co; the contact page says what to include. You can also follow Lull on Pinterest.
Credits
The Android robot is reproduced or modified from work created and shared by Google and used according to terms described in the Creative Commons 3.0 Attribution License.
Photos come from Wikimedia Commons, each in the public domain or under a Creative Commons license, and from Unsplash, under the Unsplash License. The credit under each photo names who took it, and for Commons photos the license too. Every chart on the site is ours, drawn from the same data the calculators use.