Sleep Calculator
Calculate ideal bedtimes based on 90-minute sleep cycles and your wake-up time.
Results
Waking up groggy? You are probably interrupting a sleep cycle. Sleep happens in 90-minute cycles of light sleep, deep sleep and REM. Waking up between cycles (rather than in the middle of one) makes you feel dramatically more rested. Enter your wake-up time and this calculator shows the ideal bedtimes for 3, 4, 5 or 6 complete cycles, accounting for the average 14 minutes it takes to fall asleep.
Explore all our countdown and duration calculator tools, or browse the full time and date converters & calculators.
Frequently asked questions
Adults need 7-9 hours (4-6 sleep cycles of 90 minutes each). 5 cycles = 7.5 hours and 6 cycles = 9 hours are ideal. Teenagers need 8-10 hours and children need 9-12 hours.
A sleep cycle lasts about 90 minutes and moves through light sleep (stages 1-2), deep sleep (stage 3) and REM sleep. You complete 4-6 cycles per night. Waking during deep sleep causes grogginess.
8 hours is not a multiple of 90 minutes. You wake up mid-cycle during deep sleep. Try 7.5 hours (5 cycles) or 9 hours (6 cycles) for better alignment.
Yes. The average person takes 10-20 minutes to fall asleep (sleep onset latency). We use 14 minutes as the average. If you fall asleep faster or slower, mentally adjust the bedtimes by a few minutes.
For 6 AM wake-up: 6 cycles (9h) = 8:46 PM, 5 cycles (7.5h) = 10:16 PM, 4 cycles (6h) = 11:46 PM. The 5-cycle option (10:16 PM) works best for most adults.