Sleep Cycle Calculator
Find the best time to go to bed or wake up, based on 90-minute sleep cycles. Everything runs in your browser — nothing you enter is uploaded.
Mode A — I want to wake up at
Choose a wake-up time to see your best bedtimes.
Mode B — I’m going to bed at
Choose a bedtime to see your best wake-up times.
Results assume about 15 minutes to fall asleep.
How sleep cycles work
Sleep runs in cycles of about 90 minutes. Waking up between cycles — rather than in the middle of one — usually feels better, even if you sleep a little less overall. That is why this calculator counts back or forward in whole 90-minute cycles, plus about 15 minutes to fall asleep.
For most adults, 5 cycles (7.5 hours) or 6 cycles (9 hours) are the recommended options shown above. Shorter nights of 3 or 4 cycles can help in a pinch, but they are not a substitute for regular, full sleep.
This calculator is a guide, not medical advice — persistent sleep problems deserve a doctor.
How to use this calculator
You do not need to sign up or enter personal details. Everything runs in your browser, so you can try different times in seconds and pick the result that fits your day.
For Mode A, enter the time you must wake up, for example for work or school. The calculator counts backward from that time in whole 90-minute cycles and allows about 15 minutes to fall asleep. Look first at the results marked Recommended, then choose a bedtime you can realistically keep.
For Mode B, enter the time you plan to go to bed. If you are ready now, use Going to bed now to fill in the current time. The calculator then counts forward in whole cycles and shows your best wake-up times, with the recommended options marked.
Try to keep a steady bedtime and wake time for a few days before you judge the result. A regular routine makes it easier to fall asleep and to wake feeling rested.
Worked example
The examples below use the same rules as the calculator: whole 90-minute cycles plus about 15 minutes to fall asleep.
If you want to wake at 7:00 AM, the 5-cycle bedtime is 11:15 PM. That is five cycles, or 7.5 hours, counted back from 7:00 AM, plus 15 minutes to fall asleep. You would be in bed at 11:15 PM, fall asleep at about 11:30 PM, and complete five full cycles by 7:00 AM.
If you go to bed at 10:30 PM, the 5-cycle wake time is 6:15 AM. Allow 15 minutes to fall asleep, from 10:30 PM to about 10:45 PM, then add five 90-minute cycles, or 7.5 hours, to reach 6:15 AM.
Five and six cycles are highlighted because they give most adults 7.5 or 9 hours of sleep, a full night for many people, while still ending at the end of a cycle. Three or four cycles give only 4.5 or 6 hours, so they can help on a short night but are not a good regular plan. Waking at the end of a cycle, rather than in the middle of one, is also why a slightly shorter, complete night can feel better than a longer night cut short mid-cycle.
Frequently asked questions
Why 90 minutes per cycle?
Ninety minutes is an average, not an exact rule for every person or every night. During a typical cycle, sleep moves through lighter stages, deeper sleep, and dreaming sleep, then back to lighter sleep. Your own cycles may be a little shorter or longer, so use these times as a helpful starting point.
Why are 5 or 6 cycles best?
For most adults, five cycles give 7.5 hours and six cycles give 9 hours. That range matches the amount of sleep many adults need, and both options end at a cycle boundary. Shorter options are shown for a difficult night, but they should not replace regular full sleep.
What happens if I wake mid-cycle?
Waking in the middle of a cycle, especially during deep sleep, can leave you groggy or heavy-headed for a while, even after a long night. This groggy feeling is often called sleep inertia. Waking at the end of a cycle, during lighter sleep, usually makes it easier to get up.
Does the 15-minute latency matter?
Yes, a little. If you ignore the time it takes to fall asleep, your cycles start later than planned and your alarm may fall mid-cycle. The calculator adds about 15 minutes as a simple average. If you usually take much longer to fall asleep, allow more time.
Is this medical advice?
No. This calculator is a general guide based on average cycle length. It does not diagnose sleep problems or replace medical advice. If you often struggle to fall asleep, stay asleep, or feel tired during the day, talk to a doctor.