Sleep calculator
Pick the time you need to wake up and get bedtimes that end on a full sleep cycle, or start from your bedtime and get wake times. Below that, add up your sleep debt for the past week.
Go to bed at one of these times. The first two give 7.5 to 9 hours of sleep.
Set your alarm for one of these times. The first two give 7.5 to 9 hours of sleep.
Sleep debt
h min
Sleep debt over these nights, compared with your target.
h min
No sleep debt. You slept this much more than your target.
How sleep cycles work
During the night you move through cycles of light sleep, deep sleep and REM sleep. Each cycle lasts about 90 minutes on average, but it varies between people and through the night, from about 70 to 120 minutes. Waking at the end of a cycle, during lighter sleep, can feel easier than waking out of deep sleep.
The calculator adds the time you usually take to fall asleep, then counts back or forward in 90 minute steps. Most healthy adults fall asleep in 10 to 20 minutes.
Treat the times as a guide, not a rule. Getting enough total sleep matters far more than hitting the end of a cycle. The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 or more hours a night for adults.
About sleep debt
Sleep debt is the gap between the sleep you need and the sleep you got. This calculator adds up that gap across the nights you enter. Nights where you slept more than your target count against the debt. Research suggests one long lie in does not fully undo a week of short nights, so regular sleep is the better fix.
If you often feel tired after enough sleep, snore loudly or stop breathing at night, talk to a doctor. This is not medical advice.
Questions
What time should I go to bed to wake up at 6 am?
With 15 minutes to fall asleep, try 8:45 pm for 9 hours or 10:15 pm for 7.5 hours. Enter your own wake time above for other options.
What time should I go to bed to wake up at 7 am?
With 15 minutes to fall asleep, 9:45 pm gives 9 hours and 11:15 pm gives 7.5 hours.
Is 6 hours of sleep enough?
For most adults, no. Regularly sleeping 6 hours or less is linked with worse focus, mood and health. A few people need less, but they are rare.
Can you catch up on lost sleep?
Partly. Extra sleep over a few nights helps you feel better, but it does not fully reverse the effects of chronic short sleep. A steady schedule works better.
How long is one sleep cycle?
About 90 minutes on average, with a normal range of about 70 to 120 minutes.
See your real nights
Marrow reads your sleep from Apple Health, along with HRV and resting heart rate, so you can check these numbers against the sleep your watch or ring actually recorded instead of guessing.
More free tools: HRV calculator, TDEE calculator, all calculators.