Sleep Calculator — Bedtime & Wake-Up Time
Find the best time to sleep or wake based on 90-minute sleep cycles — enter a time and get several bedtime or wake-up suggestions.
Cycle length, time to fall asleep, clock and naps are remembered in this browser; age and times are not.
Rated against the 7–9 hours a night recommended for adults; choose an age for another range.
Wake up at one of these times:
- 8:14 AM next day6 cycles · 9 h sleep · recommended
- 6:44 AM next day5 cycles · 7.5 h sleep · recommended
- 5:14 AM next day4 cycles · 6 h sleep · shorter than recommended
- 3:44 AM next day3 cycles · 4.5 h sleep · shorter than recommended
🔒 Calculated in your browser. Suggestions based on ~90-minute sleep cycles and 14 min to fall asleep — a rough guide, not medical advice. Individual sleep varies.
Wake up between sleep cycles
Sleep runs in roughly 90-minute cycles. Waking at the end of a cycle — rather than in the middle of deep sleep — tends to feel easier. Enter the time you plan to get into bed to see good wake-up times, or a target wake-up time to see when to head to bed. It also allows 14 minutes to fall asleep unless you set your own in “Time to fall asleep (minutes)”. The times are written with AM/PM on this page, and the “Clock” select switches them to “24-hour” and back.
Suggestions, not a rule
The 90-minute cycle and 14-minute latency are common averages — real sleep varies from person to person and night to night. Use the times as a guide, and aim for 5–6 full cycles (about 7.5–9 hours). Everything is calculated in your browser. The cycle length, time to fall asleep, clock and nap choice are remembered in this browser, and “Forget saved settings” clears them; your age is not kept.
Frequently asked questions
How does a sleep cycle calculator work?
It counts back or forward in whole sleep cycles from your chosen time — about 90 minutes each by default, or the length you set — plus the time you take to fall asleep (14 minutes unless you change it), so you wake near the end of a cycle rather than mid-deep-sleep.
How many sleep cycles do I need?
Most adults do well on 5–6 cycles, roughly 7.5–9 hours. The tool lists several options so you can pick what fits your schedule.
How much sleep should I get at my age?
Pick an age group and the page shows the hours the National Sleep Foundation recommends for it — naps included for young children — and offers only the bedtimes whose whole sleep cycles fall inside that range. “Any age” keeps the usual suggestions, marked against the adult range.
Can I change the cycle length, and does it say which times are best?
Yes. “Cycle length (minutes)” sets the cycle every suggestion is counted in. Each time is marked “recommended”, “shorter than recommended” or “longer than recommended” against the chosen age's range — or the adult range when no age is chosen — and only the recommended ones are in bold. Each also says whether it falls the day before, the same day or the next day, and “Add nap lengths” adds short rows of one and two cycles, marked “nap”.
Can I see the times on a 24-hour clock?
Yes. The “Clock” select, last in the row, switches every suggested time to “12-hour (AM/PM)” or “24-hour”; “Page default (12-hour)” keeps the English page's AM/PM. The choice is kept in the link, so a copied link opens on the same clock.