Sleep Sums
Free sleep calculators with the science shown: bedtime and wake-up times by sleep cycle, how much sleep you need by age, sleep cycles and REM from last night, sleep debt, nap timing, caffeine cut-off, and a jet lag plan.
Most sleep calculators give you a bedtime and no reason to believe it. Every tool here uses a published guideline, shows the arithmetic, and explains what to do with the result -- which alarm to set, how many nights it takes to clear a sleep debt, when today's last coffee has to be.
Bedtime, cycles and debt covers the nightly questions: when to sleep, what last night was made of, and what a bad week cost. Caffeine, naps and travel covers the things that move your sleep around during the day.
Bedtime, cycles & debt
What time to go to bed or wake up to finish a full 90-minute sleep cycle, allowing 14 minutes to fall asleep, with how much sleep you need at your age.
Cycles & REM last nightHow many sleep cycles you completed from the time you fell asleep and woke, and roughly how that split into light, deep and REM sleep.
Sleep debtYour sleep debt from a week of actual sleep against the need for your age, and how many nights of extra sleep it takes to pay it back.
Caffeine, naps & travel
The best nap length (20, 30 or 90 minutes) and the window in the afternoon to take it based on when you woke up, so it helps today without wrecking tonight.
Caffeine cut-off timeHow much caffeine is still in your system from each drink, using the 5-hour half-life, and the latest time you can have your last one and still fall asleep at your bedtime.
Jet lag planHow many days jet lag will last for your trip and a day-by-day plan for light, melatonin and bedtime shifts, based on time zones crossed and direction of travel.
Frequently Asked Questions
Where do the numbers come from?
Each calculator names its source on the page: the National Sleep Foundation and AASM sleep-duration consensus for how much sleep you need, the 90-minute sleep cycle and 14-minute onset allowance for bedtimes, the FDA's 5-hour caffeine half-life and 400 mg guideline, and the Lancet re-entrainment rates for jet lag. Nothing here is invented; the reasoning is shown so you can check it.
Is the 90-minute sleep cycle real?
It is a real average with a real range. Adult cycles run about 70 to 120 minutes and get longer through the night, so a bedtime built on 90-minute blocks is a sensible default rather than a precise prediction. What matters more is consistency: a fixed wake time trains your body to finish a cycle before the alarm.
Do I need an account, and is anything saved?
No account, nothing saved. Every calculation runs in your browser and nothing you type is sent anywhere.