Sleep calculator
Tell the calculator when you need to wake up, or when you plan to fall asleep, and it lists the bedtimes or wake-up times that end on a full 90-minute sleep cycle so you wake feeling rested.
Result
- Best time (5 cycles)
- 23:15 (5 cycles · 7.5 h)
- All options (6 to 3 cycles)
21:45 (6 cycles · 9 h) 23:15 (5 cycles · 7.5 h) 00:45 (4 cycles · 6 h) 02:15 (3 cycles · 4.5 h)
- How to read this
To wake up at 07:00 feeling rested, fall asleep at the end of a 90-minute cycle; these bedtimes already include the 15 minutes you take to fall asleep.
How to use this tool
- Choose whether you are planning around a wake-up time or a bedtime.
- Enter that time using the 24-hour clock.
- Adjust how long you usually take to fall asleep; 15 minutes is typical.
- Pick the option that gives you 5 or 6 cycles when you can, and set your alarm.
Good to know
- Assumes 90-minute sleep cycles; real cycles vary between people and across the night.
- This is general guidance, not medical advice. Persistent sleep problems deserve a conversation with a doctor.
Frequently asked questions
What is a sleep cycle and why 90 minutes?
A full night is made of repeating cycles that move through light sleep, deep sleep and REM sleep. Each cycle lasts roughly 90 minutes in adults, although real cycles range from about 70 to 120 minutes and lengthen through the night. Waking at the end of a cycle, during light sleep, usually feels easier than being pulled out of deep sleep.
How many cycles should I aim for?
Five cycles add up to 7.5 hours, which sits inside the 7 to 9 hours most adults need, so it is marked as the best option. Six cycles give 9 hours for people who need more. Four cycles, 6 hours, is a short night, and three cycles, 4.5 hours, is only for occasional emergencies.
Why does the calculator ask how long I take to fall asleep?
Cycles start when you actually fall asleep, not when you get into bed. Most people need 10 to 20 minutes, so the default is 15. If you usually drift off quickly, lower it; if you lie awake for half an hour, raise it. The times shown already include this buffer.
Is waking at the end of a cycle guaranteed to feel better?
No calculator can know your exact cycle length, which varies with age, stress, alcohol and how tired you are. Treat the times as sensible targets rather than precise science: a regular schedule, enough total sleep and a dark, cool room matter more than hitting an exact minute. See a doctor if sleep problems persist.
Does the calculator work across midnight?
Yes. Times wrap around the 24-hour clock, so a 07:00 wake-up with 15 minutes to fall asleep gives bedtimes of 21:45, 23:15, 00:45 and 02:15. Enter times in 24-hour format; seven in the evening is 19:00. Daylight-saving changes on the night in question are not accounted for.
Results are estimates for general information. Double-check anything important with an official source.