Sleep Cycle Calculator
Work out the best times to go to bed or wake up, counted in full 90-minute sleep cycles.
Go to bed at one of these times to wake up at 07:00
- 21:45 Recommended
- 23:15 Recommended
- 00:45
- 02:15
Based on 90-minute cycles plus 15 minutes to fall asleep.
These times are estimates based on average 90-minute sleep cycles — they are not medical advice. Real cycles vary between people and across the night. Talk to a doctor if you regularly struggle to sleep or feel tired after a full night's rest.
How it works
Sleep runs in repeating cycles of light sleep, deep sleep and REM that last roughly 90 minutes each. Waking up in the middle of a cycle — especially out of deep sleep — is what leaves you groggy, while waking at the end of one usually feels much easier. This calculator counts whole cycles for you: pick the time you must be up and it works backwards to the bedtimes that end on a cycle boundary, or pick a bedtime and it works forwards to the best wake-up times.
It also adds the time it takes you to actually drop off (15 minutes by default — adjust it if you know you fall asleep faster or slower), and you can change the cycle length between 60 and 120 minutes if you track your own sleep. Five to six cycles, about 7.5 to 9 hours, is the range most adults need, so those options are marked as recommended. Everything is calculated in your browser with plain JavaScript: nothing is uploaded, there are no accounts and no ads.
Frequently asked questions
What time should I go to bed to wake up at 7am?
Counting back full 90-minute sleep cycles and allowing 15 minutes to fall asleep, the best bedtimes for a 7:00 wake-up are 21:45 (six cycles, 9 hours), 23:15 (five cycles, 7.5 hours), 00:45 (four cycles) and 02:15 (three cycles). Five or six cycles suits most adults.
How long is a sleep cycle?
A full cycle through light sleep, deep sleep and REM lasts about 90 minutes on average, though it varies from roughly 60 to 120 minutes between people and even between cycles in one night. You can change the cycle length in the calculator if you track your own sleep.
Why does waking up between cycles feel better?
If your alarm goes off during deep sleep you wake with sleep inertia — that heavy, groggy feeling that can last half an hour. Waking at the end of a cycle, when sleep is lightest, usually feels far easier, even if you slept slightly less overall. These are estimates, not medical advice.