Sleep Calculator: Bedtime, Wake Time & Sleep Cycles

What does 11:15 PM mean?

It means that to wake at 7:00 AM after 5 full sleep cycles — 7 hours 30 minutes of sleep — you need to be asleep by 11:30 PM, and with 15 minutes to fall asleep that means getting into bed at 11:15 PM. A sleep cycle is about 90 minutes: light sleep, deep sleep, dreaming sleep, then back to light — and waking at the end of a cycle, when sleep is lightest, feels easier than waking in the middle of deep sleep. The bedtime is not a guess: 7:00 AM minus 7 hours 30 minutes is 11:30 PM, minus 15 minutes to fall asleep is 11:15 PM.

Three things to check before you trust the number

Count the time to fall asleep, or the cycles are wrong. The 15 minutes between getting into bed and falling asleep is not sleep — it comes out of the night. With 30 minutes to fall asleep the 5-cycle bedtime is 11:00 PM, not 11:15 PM, and with 45 minutes it is 10:45 PM. Most people take 10 to 20 minutes; if you take longer, put your real number in, because every minute lying awake pushes the bedtime earlier by the same minute.

Five cycles is the target, four is the floor. Five cycles is 7 hours 30 minutes, the middle of the 7 to 9 hours most adults need. Four cycles is 6 hours — enough for a night, not for a week — and three cycles is 4 hours 30 minutes, a short night that leaves a debt to repay. Six cycles is 9 hours, the top of the range, worth it after a hard week or an illness. Pick the row that matches the night you need, not the night you wish you had.

A cycle is about 90 minutes, not exactly 90. Real cycles run 80 to 110 minutes and drift through the night — the first cycles are deeper, the later ones carry more dreaming sleep — so 11:15 PM is the best bedtime on the 90-minute rule, not a promise that you will wake refreshed to the minute. Use it as a target, keep the wake time steady, and let your body settle into the rhythm.

Worked example

On the defaults: wake at 7:00 AM, 15 minutes to fall asleep.

1. Five cycles of sleep: 5 × 90 minutes = 450 minutes, 7 hours 30 minutes.
2. Asleep by: 7:00 AM minus 7 hours 30 minutes = 11:30 PM.
3. Into bed by: 11:30 PM minus 15 minutes to fall asleep = 11:15 PM.
4. Six cycles: 6 × 90 minutes = 9 hours; 7:00 AM minus 9 hours minus 15 minutes = 9:45 PM.
5. Four cycles: 4 × 90 minutes = 6 hours; 7:00 AM minus 6 hours minus 15 minutes = 12:45 AM.
6. Three cycles: 3 × 90 minutes = 4 hours 30 minutes; 7:00 AM minus 4 hours 30 minutes minus 15 minutes = 2:15 AM.
7. Latest bedtime for at least 7 hours of sleep: 11:45 PM — at 11:45 PM the sleep is 7 hours, and at 12:00 AM it is 6 hours 45 minutes.
8. Earliest wake time for at least 7 hours 30 minutes: 6:45 AM — at 6:45 AM the sleep is 7 hours 30 minutes, and at 6:30 AM it is 7 hours 15 minutes.

Every branch, checked

• Wake 6:00 AM: Wake 6:00 AM: Bedtimes for a 6:00 AM wake-up (15 min to fall asleep): 6 cycles 8:45 PM (9h 00m), 5 cycles 10:15 PM (7h 30m), 4 cycles 11:45 PM (6h 00m), 3 cycles 1:15 AM (4h 30m). wake 6:00 AM — go to bed at 10:15 PM for 5 cycles, 7 hours 30 minutes; an hour earlier than the headline, because the whole table moves with the wake time.
• Wake 8:00 AM: Wake 8:00 AM: Bedtimes for a 8:00 AM wake-up (15 min to fall asleep): 6 cycles 10:45 PM (9h 00m), 5 cycles 12:15 AM (7h 30m), 4 cycles 1:45 AM (6h 00m), 3 cycles 3:15 AM (4h 30m). wake 8:00 AM — go to bed at 12:15 AM for 5 cycles; a later wake time is a later bedtime, and the cycles stay 90 minutes apart.
• 30 minutes to fall asleep: 30 minutes to fall asleep: Bedtimes for a 7:00 AM wake-up (30 min to fall asleep): 6 cycles 9:30 PM (9h 00m), 5 cycles 11:00 PM (7h 30m), 4 cycles 12:30 AM (6h 00m), 3 cycles 2:00 AM (4h 30m). 30 minutes to fall asleep — go to bed at 11:00 PM for 5 cycles; every extra minute lying awake pushes the bedtime earlier by the same minute.
• Falls asleep instantly: Falls asleep instantly: Bedtimes for a 7:00 AM wake-up (0 min to fall asleep): 6 cycles 10:00 PM (9h 00m), 5 cycles 11:30 PM (7h 30m), 4 cycles 1:00 AM (6h 00m), 3 cycles 2:30 AM (4h 30m). falls asleep instantly — go to bed at 11:30 PM for 5 cycles; with no time to fall asleep the bedtime is 15 minutes later than the headline.
• Wake times from bedtime: Wake times from bedtime: Wake times for a 11:00 PM bedtime (15 min to fall asleep): 6 cycles 8:15 AM (9h 00m), 5 cycles 6:45 AM (7h 30m), 4 cycles 5:15 AM (6h 00m), 3 cycles 3:45 AM (4h 30m). wake times from bedtime — for an 11:00 PM bedtime, wake at 6:45 AM for 5 cycles; the same 90-minute steps, counted forward from bedtime instead of back from waking.
• Bedtime 10:00 PM: Bedtime 10:00 PM: Wake times for a 10:00 PM bedtime (15 min to fall asleep): 6 cycles 7:15 AM (9h 00m), 5 cycles 5:45 AM (7h 30m), 4 cycles 4:15 AM (6h 00m), 3 cycles 2:45 AM (4h 30m). bedtime 10:00 PM — wake at 5:45 AM for 5 cycles; an earlier bedtime is an earlier wake time, and the cycles stay 90 minutes apart.
• Wake 5:30 AM: Wake 5:30 AM: Bedtimes for a 5:30 AM wake-up (15 min to fall asleep): 6 cycles 8:15 PM (9h 00m), 5 cycles 9:45 PM (7h 30m), 4 cycles 11:15 PM (6h 00m), 3 cycles 12:45 AM (4h 30m). wake 5:30 AM — go to bed at 9:45 PM for 5 cycles; an early start needs an early night, and 5 cycles is still 7 hours 30 minutes.
• 45 minutes to fall asleep: 45 minutes to fall asleep: Bedtimes for a 7:00 AM wake-up (45 min to fall asleep): 6 cycles 9:15 PM (9h 00m), 5 cycles 10:45 PM (7h 30m), 4 cycles 12:15 AM (6h 00m), 3 cycles 1:45 AM (4h 30m). 45 minutes to fall asleep — go to bed at 10:45 PM for 5 cycles; half an hour more to fall asleep is half an hour earlier to bed.
• Wake 9:00 AM: Wake 9:00 AM: Bedtimes for a 9:00 AM wake-up (15 min to fall asleep): 6 cycles 11:45 PM (9h 00m), 5 cycles 1:15 AM (7h 30m), 4 cycles 2:45 AM (6h 00m), 3 cycles 4:15 AM (4h 30m). wake 9:00 AM — go to bed at 1:15 AM for 5 cycles; the 5-cycle bedtime passes midnight, which is fine — the cycles count back across it.
• Wake 7:37 AM, 12 minutes to fall asleep: Wake 7:37 AM, 12 minutes to fall asleep: Bedtimes for a 7:37 AM wake-up (12 min to fall asleep): 6 cycles 10:25 PM (9h 00m), 5 cycles 11:55 PM (7h 30m), 4 cycles 1:25 AM (6h 00m), 3 cycles 2:55 AM (4h 30m). fractional inputs — wake 7:37 AM, 12 minutes to fall asleep, go to bed at 11:55 PM for 5 cycles; the same arithmetic, to the minute.

The reverses, worked backwards

• Latest bedtime for at least 7 hours of sleep: 11:45 PM — at 11:45 PM the figures are Bed 11:45 PM, wake 7:00 AM (15 min to fall asleep): 7 hours of sleep — 4 full cycles and 60 minutes (sleep 420 minutes; 4 full cycles); at the later neighbor the figures are Bed 12:00 AM, wake 7:00 AM (15 min to fall asleep): 6 hours 45 minutes of sleep — 4 full cycles and 45 minutes (sleep 405 minutes; 4 full cycles); at the lower neighbor the figures are Bed 11:30 PM, wake 7:00 AM (15 min to fall asleep): 7 hours 15 minutes of sleep — 4 full cycles and 75 minutes (sleep 435 minutes; 4 full cycles) — verdict: STEP.
• Earliest wake time for at least 7 hours 30 minutes of sleep: 6:45 AM — at 6:45 AM the figures are Bed 11:00 PM, wake 6:45 AM (15 min to fall asleep): 7 hours 30 minutes of sleep — 5 full cycles and 0 minutes (sleep 450 minutes; 5 full cycles); at the earlier neighbor the figures are Bed 11:00 PM, wake 6:30 AM (15 min to fall asleep): 7 hours 15 minutes of sleep — 4 full cycles and 75 minutes (sleep 435 minutes; 4 full cycles); at the lower neighbor the figures are Bed 11:00 PM, wake 7:00 AM (15 min to fall asleep): 7 hours 45 minutes of sleep — 5 full cycles and 15 minutes (sleep 465 minutes; 5 full cycles) — verdict: STEP.
• Longest time to fall asleep for at least 7 hours of sleep: 60 min — at 60 min the figures are Bed 11:00 PM, wake 7:00 AM (60 min to fall asleep): 7 hours of sleep — 4 full cycles and 60 minutes (sleep 420 minutes; 4 full cycles); at the upper neighbor the figures are Bed 11:00 PM, wake 7:00 AM (65 min to fall asleep): 6 hours 55 minutes of sleep — 4 full cycles and 55 minutes (sleep 415 minutes; 4 full cycles); at the lower neighbor the figures are Bed 11:00 PM, wake 7:00 AM (55 min to fall asleep): 7 hours 5 minutes of sleep — 4 full cycles and 65 minutes (sleep 425 minutes; 4 full cycles) — verdict: STEP.
• Latest bedtime for at least 6 hours of sleep (wake 6:00 AM): 11:45 PM — at 11:45 PM the figures are Bed 11:45 PM, wake 6:00 AM (15 min to fall asleep): 6 hours of sleep — 4 full cycles and 0 minutes (sleep 360 minutes; 4 full cycles); at the later neighbor the figures are Bed 12:00 AM, wake 6:00 AM (15 min to fall asleep): 5 hours 45 minutes of sleep — 3 full cycles and 75 minutes (sleep 345 minutes; 3 full cycles); at the lower neighbor the figures are Bed 11:30 PM, wake 6:00 AM (15 min to fall asleep): 6 hours 15 minutes of sleep — 4 full cycles and 15 minutes (sleep 375 minutes; 4 full cycles) — verdict: STEP.
• Earliest wake time for at least 6 hours of sleep (bed 10:00 PM): 4:15 AM — at 4:15 AM the figures are Bed 10:00 PM, wake 4:15 AM (15 min to fall asleep): 6 hours of sleep — 4 full cycles and 0 minutes (sleep 360 minutes; 4 full cycles); at the earlier neighbor the figures are Bed 10:00 PM, wake 4:00 AM (15 min to fall asleep): 5 hours 45 minutes of sleep — 3 full cycles and 75 minutes (sleep 345 minutes; 3 full cycles); at the lower neighbor the figures are Bed 10:00 PM, wake 4:30 AM (15 min to fall asleep): 6 hours 15 minutes of sleep — 4 full cycles and 15 minutes (sleep 375 minutes; 4 full cycles) — verdict: STEP.
• Latest bedtime for at least 8 hours of sleep (wake 8:00 AM): 11:45 PM — at 11:45 PM the figures are Bed 11:45 PM, wake 8:00 AM (15 min to fall asleep): 8 hours of sleep — 5 full cycles and 30 minutes (sleep 480 minutes; 5 full cycles); at the later neighbor the figures are Bed 12:00 AM, wake 8:00 AM (15 min to fall asleep): 7 hours 45 minutes of sleep — 5 full cycles and 15 minutes (sleep 465 minutes; 5 full cycles); at the lower neighbor the figures are Bed 11:30 PM, wake 8:00 AM (15 min to fall asleep): 8 hours 15 minutes of sleep — 5 full cycles and 45 minutes (sleep 495 minutes; 5 full cycles) — verdict: STEP.

What the defaults assume

The defaults are a 7:00 AM wake-up, an 11:00 PM bedtime and 15 minutes to fall asleep — a working day that starts at seven, a normal night — and the best bedtime is 11:15 PM for 5 full cycles, 7 hours 30 minutes of sleep. They are a starting point, not a prescription: your wake time may be 5:30 AM, your time to fall asleep may be 45 minutes, and the right answer for you is the one your numbers describe. Change the wake time, the bedtime and the minutes to fall asleep to your own and the calculator recomputes instantly. Take the wake time, subtract the cycles, subtract the time to fall asleep.

These notes repeat in every explainer section because this page is built to be read start to finish: the defaults are one night, not a standard; count the time to fall asleep, or the cycles are wrong; five cycles is the target, four is the floor; and a cycle is about 90 minutes, not exactly 90.

Output · formula · meaning

Who uses this

• An early riser with a 6:00 AM alarm — go to bed at 10:15 PM for 5 cycles, 7 hours 30 minutes, instead of guessing at midnight and waking mid-cycle.
• A shift worker sleeping at odd hours — bedtime 6:00 AM means a 1:45 PM wake time for 5 cycles, and the arithmetic works the same at any hour.
• A parent working out a child's bedtime — a 6:45 AM school start with 6 cycles is 9:30 PM in bed, 15 minutes to fall asleep included.
• Anyone catching up on sleep — the latest bedtime for at least 7 hours is 11:45 PM, and 12:00 AM is already 6 hours 45 minutes, so fifteen minutes matters.

Accuracy & limitations

The calculator counts in exact 90-minute cycles and exact minutes — every bedtime on this page is checked against an independent model, and the times are whole minutes, so there is no rounding to mislead you. What it cannot do is measure your real cycles: they run 80 to 110 minutes, drift through the night, and change with age, stress and illness, so 11:15 PM is the best bedtime on the 90-minute rule, not a guarantee. It also counts one unbroken stretch — waking in the night, a baby, a snoring partner, all come out of the total, and the calculator cannot see them. It is not medical advice: persistent trouble falling asleep, loud snoring or daytime sleepiness are worth a clinician, not a calculator. And the page prints the exact minute counts so the rounding does not mislead you — the 5-cycle bedtime is 11:15 PM, minute 1395.

Cite this calculator

Sleep comes in 90-minute cycles. On the defaults — wake at 7:00 AM, 15 minutes to fall asleep — go to bed at 11:15 PM for 5 full cycles, 7 hours 30 minutes of sleep. Latest bedtime for at least 7 hours of sleep: 11:45 PM. Earliest wake time for at least 7 hours 30 minutes of sleep: 6:45 AM. Longest time to fall asleep for at least 7 hours of sleep: 60 minutes. Latest bedtime for at least 6 hours of sleep (wake 6:00 AM): 11:45 PM. Earliest wake time for at least 6 hours of sleep (bed 10:00 PM): 4:15 AM. Latest bedtime for at least 8 hours of sleep (wake 8:00 AM): 11:45 PM. Source: Bright Side Kit, brightoolbox.com.

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