Sleep Cycle
Calculator
Enter your wake-up time. Get the ideal bedtimes based on 90-minute sleep cycles — so you wake feeling rested, not groggy. No account. No data collected. Runs entirely in your browser.
Recommended bedtimes — go to sleep at
How the calculator works
Sleep happens in repeating cycles of roughly 90 minutes. Each cycle moves through four stages. Waking at the end of a complete cycle — rather than mid-cycle — is what makes the difference between springing out of bed and hitting snooze six times.
The calculator works backwards from your wake-up time in 90-minute steps, adding a 14-minute buffer for the average time it takes to fall asleep. It gives you five bedtime options — from 4.5 hours (minimum, for short nights) to 9 hours (ideal for recovery).
The sleep onset buffer
Most people don't fall asleep the instant they close their eyes. Research puts average sleep onset at 10–20 minutes. We use 14 minutes. This means the bedtime shown is when you should get into bed, not when you expect to be asleep.
Frequently asked questions
How many sleep cycles do I need?
Most adults need 5–6 complete cycles per night (7.5–9 hours). Fewer than 4 cycles (6 hours) is widely associated with reduced cognitive function and mood. The exact number varies by age and individual — use the 5-cycle or 6-cycle bedtime as your target.
What if I wake up groggy even after a full night?
Sleep inertia (the grogginess on waking) is usually caused by waking mid-cycle. If you're still experiencing it, try adjusting your bedtime by 15–20 minutes earlier or later to better align with your personal cycle length, which may differ slightly from the 90-minute average.
Does this work for naps?
Yes. For naps, aim for either 20 minutes (before entering deep sleep) or a full 90-minute cycle. Waking from deep sleep (N3) mid-cycle causes the worst grogginess. A 20-minute nap catches only N1/N2 and leaves you refreshed.
Is 90 minutes exact?
No — individual cycles range from 80 to 110 minutes. 90 minutes is the well-established average used in sleep research. If the calculated times don't feel right for you, try shifting by 10–15 minutes in either direction to find your personal rhythm.
Calculate by wake-up time
Select your wake-up time for a pre-calculated bedtime guide.