Find the best times to go to bed or wake up based on 90-minute sleep cycles, so you are more likely to wake up between cycles and feel refreshed.
How sleep cycles work
During the night, you move through repeating sleep cycles of light sleep, deep sleep and REM (dream) sleep. Each cycle lasts roughly 90 minutes, although it varies from about 70 to 120 minutes between people and through the night. Waking at the end of a cycle, in lighter sleep, usually feels easier than being jolted out of deep sleep.
How the calculator works
Bedtime = wake-up time − (cycles × 90 min) − time to fall asleep
It shows options for 6, 5, 4 and 3 cycles (9, 7.5, 6 and 4.5 hours of sleep).
Worked example
To wake at 6:30 AM and allowing 15 minutes to fall asleep:
- 6 cycles (9 hours): go to bed at 9:15 PM
- 5 cycles (7.5 hours): go to bed at 10:45 PM
- 4 cycles (6 hours): go to bed at 12:15 AM
How much sleep do you need?
Most adults need 7 or more hours a night according to the CDC and the American Academy of Sleep Medicine. Teenagers need 8 to 10 hours. Consistent sleep and wake times matter as much as the total.
Tips for better sleep
- Keep a regular schedule, even on weekends.
- Keep your bedroom cool, dark and quiet.
- Limit caffeine in the afternoon and screens before bed.
- Get daylight in the morning to help set your body clock.
Frequently asked questions
Are sleep cycles exactly 90 minutes?
No. 90 minutes is an average. If you wake up groggy, try shifting your bedtime by 15 minutes.
Is 6 hours of sleep enough?
For most adults, regularly sleeping 6 hours or less is linked to poorer health and alertness. Aim for 7 to 9.
Related tools
General guidance only. If you regularly have trouble sleeping or feel tired despite enough sleep, talk to a healthcare professional.