Sleep Cycle Calculator
Formula
Wake Time = Bedtime + (Cycles × 90min) + 15min
Sleep cycles last roughly 90 minutes. Waking between cycles helps you feel refreshed. 15 minutes is added for falling asleep. The recommended option (5 cycles = 7.5 hours) is shown as the primary answer.
How to use
- Enter your planned bedtime in the Bedtime Hour (24h) field.
- Set the Bedtime Minutes field to match.
- Read the suggested wake-up times for 4, 5, and 6 cycles.
Example
Going to bed at 23:00 (11:00 PM), the 5-cycle option adds 7.5 hours plus 15 minutes, suggesting you wake at 6:45 AM feeling refreshed.
Frequently Asked Questions
How many sleep cycles do I need?
Most adults need 5-6 cycles (7.5-9 hours). 4 cycles (6 hours) is the bare minimum some people get by on, but most adults function best on at least 7 hours.
Why 90-minute cycles?
Each cycle goes through light sleep, deep sleep, and REM. Waking mid-cycle (especially deep sleep) causes grogginess.
What does the 15 minutes account for?
The average person takes about 15 minutes to fall asleep. The wake times are calculated from when you actually fall asleep, not when you get into bed.
What time should I go to bed to wake up at a set time?
Work backward from your alarm in 90-minute blocks and add about 15 minutes to fall asleep. To wake at 6:30 a.m. with five cycles (7.5 hours), you'd fall asleep around 11:00 p.m., meaning you should be in bed by about 10:45 p.m. Targeting the end of a cycle this way helps you wake during light sleep instead of in the middle of deep sleep.
Do naps follow the same 90-minute cycle?
Partly — a full 90-minute nap lets you complete one cycle and wake refreshed, while a short 20-minute power nap keeps you in light sleep and avoids grogginess. The times to avoid are in between, around 45 to 60 minutes, when you're likely to wake during deep sleep and feel worse. Late-afternoon naps can also make it harder to fall asleep at your normal bedtime.