Pick the time your alarm goes off and see when to be in bed, or start from your bedtime and see when to wake. Each option is a whole number of roughly 90-minute cycles, plus the time it takes you to drift off.
To wake up at 7:00 AM, with lights out at the time shown:
Real cycles are not all the same length: they differ between people and through the night, so these times are estimates, not a guarantee of waking between cycles.
Not medical advice. An estimate for healthy adults. If you often sleep badly or feel sleepy in the day, talk to a doctor.
Through the night you move through repeating cycles of lighter sleep, deep sleep and REM (dreaming) sleep. The first REM period usually arrives about 90 minutes after you fall asleep (NINDS). Waking near the end of a cycle, rather than in the middle of deep sleep, tends to feel easier, so the calculator counts back from your alarm in whole cycles and adds the time it takes you to fall asleep.
With the defaults, a 7:00 AM alarm gives lights out at 11:15 PM for five cycles: 15 minutes to drift off, then 7 hours 30 minutes asleep. Choose Bedtime to work forwards instead, or press Now if you are heading to bed.
Time to fall asleep: use what is normal for you. The National Sleep Foundation counts falling asleep within 30 minutes as a sign of good sleep quality in adults. Cycle length: 90 minutes is the usual rule of thumb, but in a study of over 6,000 recorded cycles the median was 96 minutes, with wide differences between people (Cajochen et al., 2024). If you often wake groggy, try 95 or 100.
The suggested option is the shortest night that still gives the 7 or more hours the AASM and Sleep Research Society recommend for adults (Watson et al., 2015). Children and teenagers need more: see sleep needs by age.
Each tool has its own page, works offline once loaded, and links the research behind its numbers.
Two free tools from elsewhere for the screen time that happens before bed.
Trying a free sleep sounds app or downloading a bedtime guide that insists on an email address? CleanTempMail gives you a disposable inbox in one click, with no account, and it clears itself after three days.
Open a temporary inboxFound a bargain on blackout blinds or a white-noise machine from a shop you have never heard of? WebTraceCheck's free tools show a domain's registration details and run a website audit before you hand over card details.
Look up a shop's domainFor most adults, five cycles (about 7.5 hours) or six (about 9) both meet the 7-hour minimum. Four cycles is only 6 hours: an easier wake-up does not make up for the missing sleep.
Your cycles may be longer or shorter than the setting, the time it takes you to fall asleep varies, and an irregular schedule makes waking harder. The AASM advises getting up at the same time every day, weekends included.
If you are still awake after about 20 minutes, the AASM suggests getting up and doing something quiet in dim light until you feel sleepy. If trouble sleeping goes on for weeks, talk to a doctor; a sleep diary helps them see the pattern.