Wake Up Time Calculator
Find bedtimes and wake times that fall at the end of 90-minute sleep cycles, so you wake up refreshed.
How it works
sleep block = cycles × 90 min + fall-asleep buffer · bedtime = wake − block · wake = bedtime + block
Sleep runs in cycles of roughly 90 minutes, moving from light to deep to REM sleep and back. Waking at the end of a cycle — rather than mid-deep-sleep — is what leaves you feeling refreshed instead of groggy. The calculator adds a buffer for the time it takes you to actually fall asleep, then steps back or forward in 90-minute blocks, so each suggested time lands at a cycle boundary. Five to six cycles (7.5 to 9 hours) suits most adults.
Worked example
To wake at 07:00 with a 15-minute fall-asleep buffer: 5 cycles need 7.5 hours of sleep plus 15 minutes, so lights out at about 23:15. Six cycles (9 hours) points to 21:45; four cycles (6 hours) to 00:45.
Frequently asked questions
Is every sleep cycle exactly 90 minutes?
No — 90 minutes is the average, and real cycles range from about 70 to 120 minutes and shift through the night. Treat the times as a guide, not a guarantee, and adjust to what works for you.
How many cycles should I aim for?
Most adults do best on 5 to 6 cycles, which is 7.5 to 9 hours. Four cycles (6 hours) is a lighter night; three (4.5 hours) is a short-sleep fallback, not a habit.
Why add a fall-asleep buffer?
Because you do not fall asleep the instant you lie down. Adding the time it typically takes you to drift off means the cycles are counted from when you actually sleep, not from when you get into bed.
Related calculators
This is a general sleep-timing guide based on average 90-minute cycles, not medical advice. Persistent sleep problems should be discussed with a doctor.