How it works
Pick the time you must get up, or start from right now. The calculator counts back or forward in full 90-minute sleep cycles and adds about 15 minutes to fall asleep.
Bedtime = alarm − 15 min − 90 min × cycles
Tips
- Five cycles (7.5 hours) suits most adults; six (9 hours) after heavy days.
- Keep the same wake time every day, weekends included — regularity beats total hours.
- Screens, caffeine and alcohol in the evening make falling asleep harder.
Standards and sources
- 90-minute ultradian sleep cycles (general sleep science consensus)
- Reference only — not medical advice; see a doctor for sleep disorders
Last reviewed October 8, 2026
Frequently asked questions
Why 90 minutes?
A full sleep cycle — light sleep, deep sleep and REM — lasts about 90 minutes for most adults. Waking at the end of a cycle tends to feel less groggy than being woken mid-cycle.
Why is 15 minutes subtracted?
Most people need roughly a quarter of an hour to fall asleep, so the calculator counts back from there. If you usually take longer, go to bed a little earlier.
How many cycles do I need?
Most adults do well on 5 to 6 cycles (7.5 to 9 hours). The calculator marks 5 cycles as a balanced default, but individual needs vary.
Is this medical advice?
No. It's a simple rhythm guide. If you snore heavily, gasp at night or feel exhausted despite enough sleep, talk to a doctor.