Tool · Sleep
Sleep calculator
Sleep runs in cycles of roughly 90 minutes. Waking between cycles feels better than waking in the middle of one. Pick a direction and work backwards.
Bedtimes below give you whole cycles, ending between them rather than inside one.
How this is calculated
Each cycle is counted as 90 minutes: light sleep, deep sleep, then REM. Most people take about 15 minutes to fall asleep, so that time is added before the first cycle starts. The tool then subtracts whole cycles from your wake time.
The four options it shows are 6, 5, 4 and 3 cycles — roughly 9, 7.5, 6 and 4.5 hours of sleep. Six is not automatically the right answer: for many adults 7–9 hours is the range, and a consistent schedule matters more than squeezing in one more cycle.
What it cannot do
A calculator cannot see your sleep stages, your caffeine, or the baby in the next room. Treat the numbers as a starting point you can test, not a diagnosis. If you wake unrefreshed for weeks, that is worth a conversation with a clinician rather than a better bedtime calculator.
Two things that beat any calculator
- A fixed wake time, seven days a week. The bedtime follows from it; the reverse does not work as well.
- Twenty minutes less screen before bed. The 90-minute cycle only helps if you actually fall asleep at the time you planned.
Want to see which state you are in when sleep goes wrong? Take the 60-second quiz — the Deepwell and Driftwood zones are the two that show up after bad nights.
For information only — not medical advice. All tools