CalculatorsSleep, cycle and pregnancySleep calculator
Sleep calculator
Work back from when you have to be up, in whole sleep cycles, with the time it really takes you to drift off.
23:15
- 6 cycles
- 21:459 hours asleep
- 5 cycles
- 23:157½ hours asleep
- 4 cycles
- 00:456 hours: under the 7 adults need
See the working
Bedtime = 07:00 − 15 min to fall asleep − 5 × 90 min = 23:15Sleep cycles run about 90 minutes on average and vary through the night. Treat these as a starting point: a steady wake time and seven or more hours matter more than hitting a cycle exactly.
How it works
Sleep runs in cycles of about 90 minutes. Waking at the end of one tends to feel easier than waking from deep sleep. So this counts back in whole cycles from your wake time, and adds how long you usually take to fall asleep.
It's a useful rule of thumb, not a law: real cycles run from about 70 to 120 minutes and change through the night.
What matters more than timing
Sleep experts recommend seven hours or more for adults. Getting that, regularly, and getting up at the same time each day, matters more than landing exactly on a cycle. If you wake around 3am most nights, or snore, or feel tired after a full night, that's worth a look with your doctor.
Questions
What time should I go to bed if I wake at 7?
For five cycles (7½ hours) and 15 minutes to fall asleep, about 23:15.
Is it better to wake after a whole cycle?
It can feel easier, but the evidence is modest. Total sleep and a steady schedule count for more.
How much deep sleep do I need?
It varies, and it falls with age. Many adults get about 13 to 23% of the night. Wearables estimate this roughly.
Why do I wake up at 3am?
Common reasons include alcohol, stress, a late meal, and a natural light stretch between cycles. If it keeps happening, tracking what those nights share can help.
Sources
Written by LifeFrom from the sources above, and not yet reviewed by a clinician. An estimate for your own understanding: it doesn't diagnose or treat anything, and it doesn't replace your doctor.
