Sleep Calculator
Waking up at the end of a sleep cycle helps you feel less groggy. Pick a wake-up time or a bedtime and get the best times to sleep or set your alarm.
How it works
To find a bedtime, the calculator starts at your wake-up time, steps back in 90-minute cycles and then subtracts the time it takes you to fall asleep. To find an alarm time, it does the reverse. The highlighted options give you 5 or 6 full cycles, which lines up with the 7-9 hours most adults need.
Recommended sleep by age
| Age | Recommended sleep |
|---|---|
| 6-13 years | 9-11 hours |
| 14-17 years | 8-10 hours |
| 18-64 years | 7-9 hours |
| 65 and older | 7-8 hours |
Naps work best when kept under about 20 minutes. Set a timer so you don't oversleep.
General guidance only, not medical advice. If you regularly struggle to sleep or feel exhausted, talk to a doctor.
Frequently asked questions
Why does the calculator use 90-minute cycles?
Through the night you move through light sleep, deep sleep and REM (dreaming) sleep in cycles, usually 4 to 6 of them, each lasting about 90 minutes on average. Waking up in the middle of deep sleep tends to leave you groggy, while waking near the end of a cycle usually feels easier. Real cycles range from about 70 to 120 minutes, so try it for a few days and fine-tune.
What is the "time to fall asleep" setting?
Most people take 10 to 20 minutes to actually fall asleep after getting into bed. The calculator adds that time (15 minutes by default) so the bedtimes it suggests are when to get into bed, not when sleep starts. If you usually take longer, change the number.
How many hours of sleep do I need?
The National Sleep Foundation recommends 7-9 hours for adults aged 18-64, 7-8 hours for those 65 and older, 8-10 hours for teens aged 14-17 and 9-11 hours for children aged 6-13. Getting enough sleep matters more than hitting a cycle exactly, which is why 5 cycles (7.5 hours) or 6 cycles (9 hours) are highlighted.