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Sleep calculatorWake up between sleep cycles
Sleep runs in ~90-minute cycles. Waking at the end of one — instead of mid-deep-sleep — is what stops you feeling groggy. Pick a time below.
To wake at 7:00 am, fall asleep at one of these times:
Times allow ~15 minutes to fall asleep. The highlighted options give a full 7.5–9 hours of sleep. Had a late coffee? Check it with the caffeine half-life calculator.
Why 90 minutes matters
Through the night you move through repeating ~90-minute cycles: light sleep → deep (slow-wave) sleep → REM. Most adults complete 5 to 6 cycles a night.
If your alarm goes off in the middle of deep sleep, you wake with sleep inertia — that heavy, foggy feeling that can last 15–30 minutes. Timing your alarm to the end of a cycle, even if it means slightly less total sleep, often leaves you feeling sharper.
- 5 cycles ≈ 7.5 hours — a solid night for most adults
- 6 cycles ≈ 9 hours — full recovery, ideal after sleep debt
- 4 cycles ≈ 6 hours — a short night that still ends cleanly
Cycle length varies person to person (80–110 min). Use these as smart starting points, then adjust to how you actually feel.
Protect your cycles
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Frequently asked questions
What is a sleep cycle?
About 90 minutes of light → deep → REM sleep. A full night is 5–6 cycles. Waking at the end of one helps you avoid grogginess.
What time should I go to bed to wake at 7 am?
Roughly 9:46 pm, 11:16 pm or 12:46 am — each a whole number of 90-minute cycles before 7 am, plus 15 minutes to fall asleep.
Is it better to sleep less but wake at the cycle's end?
Often yes for grogginess — waking from light sleep feels easier than from deep sleep. But don't make short nights a habit; total sleep still matters for health.