Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles — so you wake up refreshed, not groggy.
Heading to bed right now? We'll count 15 minutes to fall asleep, then show the best times to wake up.
How the sleep cycle math works
Sleep runs in cycles of about 90 minutes, moving from light sleep through deep sleep to REM and back. Waking up at the end of a cycle feels refreshing; waking mid-cycle — especially in deep sleep — is what causes grogginess.
- "I wake up at…" — counts back in 90-minute steps from your alarm, minus 15 minutes to fall asleep, suggesting bedtimes for 4, 5, or 6 full cycles (6, 7.5, or 9 hours of sleep).
- "I go to sleep now" — starts from the current time plus 15 minutes of sleep latency, then projects the best wake-up times at complete-cycle boundaries.
- "I go to bed at…" — adds 15 minutes of latency to your bedtime, then lists wake-up times after 4–6 full cycles.
Most adults do best with 5–6 cycles (7.5–9 hours). Timing is only half the story — a consistent schedule, a dark cool room, and limited evening caffeine matter just as much.
Frequently asked questions
How many sleep cycles do I need per night?
Most adults do best with 5–6 full cycles, which is 7.5–9 hours of sleep. Waking at the end of a cycle rather than in the middle of one is what makes you feel refreshed.
Why does the calculator add 15 minutes to fall asleep?
About 15 minutes is the average time it takes a healthy adult to fall asleep (sleep latency). The calculator counts back from when you plan to be asleep, not just when you get into bed.
What if I still feel tired after a full number of cycles?
Sleep quality matters as much as timing: keep a consistent schedule, limit caffeine after midday, dim lights before bed, and keep the room cool and dark. Persistent fatigue is worth discussing with a doctor.
Can I use this sleep calculator for naps?
Yes — either take a short 20-minute power nap that stays in light sleep, or a full 90-minute nap covering one complete cycle, so you wake at a natural boundary instead of mid-cycle.