Sleep Calculator
Wake up between sleep cycles, not in the middle of one. Choose whether you're setting a wake-up time or a bedtime, and get the times that let you complete full 90-minute cycles.
Sleep isn't uniform — it moves through repeating cycles of light sleep, deep sleep and REM, each lasting roughly 90 minutes. Waking at the end of a cycle, when sleep is lightest, tends to feel easy and refreshing. Waking in the middle of deep sleep is what leaves you groggy, even after a long night. This calculator counts backward or forward in 90-minute cycles so your alarm lands at a natural break.
How the sleep cycle calculation works
The tool assumes a 90-minute cycle and adds the time it takes you to actually fall asleep (about 14 minutes on average). Working from your wake-up time, it counts back whole cycles; working from your bedtime, it counts forward.
Wake time = Bedtime + time to fall asleep + (cycles × 90 min)
| Cycles | Time asleep | Best for |
|---|---|---|
| 6 cycles | 9 hours | Teens, recovery, catching up |
| 5 cycles | 7.5 hours | Most adults — a full night |
| 4 cycles | 6 hours | A shorter but complete night |
| 3 cycles | 4.5 hours | A minimum — naps or emergencies |
How much sleep do you need?
Most adults do best on 7 to 9 hours a night, which is five to six full cycles. Teenagers need more (8–10 hours), and school-age children more still. The cycle approach is a guide, not a rule — the number of hours matters more than hitting an exact cycle, so use these times as targets rather than something to stress over.
| Age group | Recommended sleep |
|---|---|
| Teenagers (14–17) | 8–10 hours |
| Adults (18–64) | 7–9 hours |
| Older adults (65+) | 7–8 hours |
Worked example
You want to wake up at 7:00 AM and you usually take about 14 minutes to drift off. Counting back:
| 6 cycles (9 h) → asleep by | 10:00 PM, in bed 9:46 PM |
| 5 cycles (7.5 h) → asleep by | 11:30 PM, in bed 11:16 PM |
| 4 cycles (6 h) → asleep by | 1:00 AM, in bed 12:46 AM |
So going to bed around 11:16 PM lines you up for five complete cycles and a 7:00 AM wake-up.
Tips for waking up refreshed
Cycle timing helps most when the rest of your sleep hygiene is solid. Keep a consistent schedule, even on weekends, so your body clock stabilises. Avoid caffeine within about six hours of bed, dim screens in the last hour, and keep the room cool and dark. If you regularly wake unrefreshed despite enough hours, that can signal a sleep problem worth discussing with a doctor.