Sleep Calculator
Best times to sleep and wakeRuns locally · nothing uploaded
Go to bed at
21:45
6 cycles · 9 h
★ Best
23:15
5 cycles · 7.5 h
★ Best
00:45
4 cycles · 6 h
02:15
3 cycles · 4.5 h
A sleep cycle lasts about 90 minutes, and waking at the end of one usually feels better. Adults need 7–9 hours (5–6 cycles).
Estimates based on general formulas, for information only. Not a substitute for professional medical advice, diagnosis or treatment.
Also works as:bedtime calculatorsleep cycle calculatorwhen to wake up
How it works
When to use it
- Work back from your alarm to a bedtime that ends on a full sleep cycle.
- Find good wake-up times from a given bedtime.
Formula
Bedtime = wake time − cycles × 90 min − time to fall asleepWake time = bedtime + time to fall asleep + cycles × 90 minOptions for 3–6 cycles (4.5–9 hours).
Worked example
Given: Wake at 7:00, 15 minutes to fall asleep
- 6 cycles: 7:00 − 9 h − 15 min = 21:45.
- 5 cycles: 7:00 − 7.5 h − 15 min = 23:15.
Result: Go to bed at 9:45 pm or 11:15 pm.
Reading the result
- Waking at the end of a cycle, in light sleep, usually feels easier.
- Adults generally need 7–9 hours a night.
Limitations
- 90 minutes is an average; cycles range roughly 70–120 minutes and vary through the night.
- See a sleep specialist for persistent insomnia, loud snoring or daytime sleepiness.
Sources
- Hirshkowitz M, et al. Sleep Health. 2015;1(1):40–43.
How to use
- 1Choose wake-up or bedtime mode.
- 2Enter the time and how long you take to fall asleep.
- 3Pick a recommended time.
FAQ
Why 90 minutes?
A full sleep cycle averages about 90 minutes; waking at the end of one feels less groggy.
How many cycles do I need?
Most adults need 5–6 cycles (7.5–9 hours).