What time will I wake up rested?
Enter the time you're going to bed. We calculate ideal wake-up times based on complete 90-minute cycles.
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Why these exact times
Sleep unfolds in successive ~90-minute cycles alternating light, deep and REM sleep. Waking up mid-cycle, especially during deep sleep, causes sleep inertia: grogginess and confusion that can last up to 30 minutes. Waking at the end of a cycle makes the transition to alertness far easier.
Frequently asked questions
Should I aim for exactly 8 hours?
Not necessarily — 8h doesn't always match a whole number of cycles. Aiming for 7h30 (5 cycles) or 9h (6 cycles) is often more effective.
Does this change with age?
Cycles stay around 90 minutes in adults, but the number of cycles needed varies with age — see our sleep-by-age guide.
Want to go further?
Explore our guides and other calculators.