Sleep Calculator
Bedtimes or wake times aligned to full 90-minute sleep cycles.
Find the best bedtime for a target wake-up time, or the best wake-up times if you're going to bed now — aligned to full 90-minute sleep cycles so you wake up feeling less groggy.
How the sleep calculator works
Sleep moves through repeating cycles of light sleep, deep sleep and REM (dreaming) sleep, each lasting about 90 minutes on average. Waking at the end of a cycle, when sleep is lighter, usually feels easier than being pulled out of deep sleep. The calculator counts back (or forward) in 90-minute cycles and adds 15 minutes for the time it takes to fall asleep.
Examples
You need to wake up at 7:00 AM. Go to bed at:
| Bedtime | Cycles | Sleep |
|---|---|---|
| 9:45 PM | 6 | 9 hours |
| 11:15 PM | 5 | 7.5 hours |
| 12:45 AM | 4 | 6 hours |
| 2:15 AM | 3 | 4.5 hours |
You're going to bed at 11:00 PM. Set your alarm for 8:15 AM (6 cycles), 6:45 AM (5 cycles), 5:15 AM (4 cycles) or 3:45 AM (3 cycles).
Tips for better sleep
- Keep a consistent schedule, including weekends, so your body learns when to get sleepy.
- Dim screens and lights in the hour before bed.
- Watch caffeine late in the day, since its effects can last for hours.
- Keep the bedroom cool, dark and quiet.
If you regularly feel unrested despite enough time in bed, talk to a doctor — ongoing sleep problems can have medical causes.
Frequently asked questions
Why 90-minute cycles?
Sleep happens in cycles of light, deep, and REM sleep lasting about 90 minutes each. Waking up at the end of a cycle (rather than in the middle of deep sleep) tends to feel less groggy.
Why does it add 15 minutes?
That accounts for the average time it takes to actually fall asleep after getting into bed.
How many hours of sleep do adults need?
US health guidance recommends at least 7 hours a night for most adults. Five full cycles (7.5 hours) or six (9 hours) fit that well; three or four cycles are better kept for occasional short nights.
Are sleep cycles always exactly 90 minutes?
No — 90 minutes is an average. Real cycles vary from person to person and through the night, so treat the suggested times as a helpful guide rather than an exact schedule.
What if I fall asleep faster or slower than 15 minutes?
Shift the suggested times by the difference. If you usually fall asleep in 5 minutes, you can go to bed about 10 minutes later than the suggested bedtime.