How to use the Sleep Calculator
- Choose I want to wake up at or I'm going to bed at (or tap Sleep now).
- Set the time, and how long you usually take to fall asleep (15 minutes is typical).
- Pick one of the suggested times. The ones with 5 or 6 full cycles are best for most adults.
- Set your alarm for that time.
How sleep cycles work
Through the night, sleep moves through light sleep, deep sleep and dreaming (REM) sleep in cycles that last roughly 90 minutes, though they vary between about 70 and 120 minutes from person to person and night to night. Waking at the end of a cycle, during light sleep, tends to feel easier than being woken from deep sleep.
How much sleep do you need?
Most adults need 7–9 hours a night. That's about five or six cycles, which is why those times are highlighted. Teenagers usually need 8–10 hours, and children more.
Good to know
- These times are a guide, not a guarantee: cycle lengths differ, so adjust by 10–15 minutes if you still wake up groggy.
- A regular wake-up time, even at weekends, helps more than any calculator.
- If you're often exhausted however long you sleep, talk to a doctor: it can be a sign of a sleep disorder.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, though each person's cycles vary between about 70 and 120 minutes.
What time should I go to bed to wake up at 7 am?
For six full cycles plus 15 minutes to fall asleep: about 9:45 pm. For five cycles: about 11:15 pm.
Is it better to sleep 6 or 7 hours?
Most adults need 7–9 hours. If you're short of time, ending at a full cycle (6 hours, or 7.5 hours) can feel better than waking in the middle of one.
Does it work for naps?
Yes: a 20-minute nap, or a full 90-minute cycle, usually avoids waking from deep sleep.
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