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Sleep Calculator
Find the best bedtime for your wake-up time, or the best time to wake up if you go to bed now, using 90-minute sleep cycles and 15 minutes to fall asleep. Plus simple habits for better sleep.
Sleep calculator
Sleep comes in cycles of about 90 minutes. Waking at the end of a cycle can feel easier.
Go to bed at
9:15 pm
6 cycles · 9.0 h sleep ✅
Go to bed at
10:45 pm
5 cycles · 7.5 h sleep ✅
Go to bed at
12:15 am
4 cycles · 6.0 h sleep
Times include about 15 minutes to fall asleep. Adults need at least 7 hours a night, so the 7.5 and 9 hour options are best for most people.
Simple habits for better sleep
- Keep the same wake-up time every day, weekends too.
- Get daylight in the morning and keep the bedroom dark, cool and quiet.
- Stop caffeine about 8 hours before bed and avoid big meals late at night.
- Put screens away 30–60 minutes before sleep.
✅ Rules last checked:
📚 Official sources: CDC: About sleep
We build every tool from the official rules and re-check them when they change. Always confirm with the official source before you rely on a result.
🛠️ Spotted a mistake or an out-of-date rule? Tell us
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Questions people ask
How much sleep do adults need?+
At least 7 hours a night for adults 18 to 60 (CDC). Teens and children need more.
Why 90-minute cycles?+
Sleep moves through light, deep and dream (REM) stages in cycles of about 90 minutes. Waking at the end of a cycle, rather than in deep sleep, can make you feel less groggy.
Why add 15 minutes?+
Most people take around 10 to 20 minutes to fall asleep, so the calculator adds 15 minutes before your first cycle starts.
What if I still feel tired?+
Cycle length is different for everyone. Try moving your bedtime 15 minutes earlier for a week. If you're often very sleepy in the day, snore loudly or can't sleep most nights, talk to a doctor.