Sleep Calculator
Wake up refreshed by aligning with your sleep cycles. Choose whether you're setting a wake time or a bedtime, and we'll suggest times built on 90-minute cycles (plus 15 minutes to fall asleep).
Example: with Time 07:00 → 6 cycles · 9 hours: 9:45 PM.
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outWhy 90-minute cycles
Sleep moves through cycles of roughly 90 minutes, ending in light sleep. Waking at the end of a cycle — rather than mid-cycle — tends to feel more refreshing than the same amount of sleep cut off at a deep stage. The suggestions add about 15 minutes to fall asleep, then count whole cycles from 3 up to 6. Most adults do best on 5–6 cycles (7.5–9 hours).
Napping: if you nap during the day, keep it under about 30 minutes — longer naps let you drop into deep sleep, so waking from one can leave you groggy (sleep inertia) rather than refreshed. Napping too late in the afternoon or evening can also make it harder to fall asleep at your planned bedtime.
Recommended sleep by age (CDC guidelines)
How it’s calculated
Built on ~90-minute sleep cycles plus ~15 minutes to fall asleep; it suggests bedtimes or wake times for 3–6 full cycles (about 4.5–9 hours), in both directions — enter a wake-up time to get bedtime options, or enter a bedtime to get wake-time options.
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Worked example
To wake at 7:00 AM, good bedtimes are about 9:45 PM (6 cycles) or 11:15 PM (5 cycles).
Common mistakes
- Treating 90-minute cycles as exact for everyone.
- Forgetting the ~15 minutes it takes to fall asleep.
- Napping too long or too late, which can undo a well-timed bedtime.
Frequently asked questions
Are sleep cycles exactly 90 minutes?
It's an average — real cycles range from about 80 to 110 minutes and shift through the night. Treat the times as helpful targets, not guarantees.
How long to fall asleep?
The calculator assumes about 15 minutes. If you usually take longer, shift your bedtime earlier accordingly.
How many cycles should I aim for?
Most adults feel best with 5–6 cycles, which is 7.5–9 hours of sleep.
How long should a nap be?
Keep naps under about 30 minutes. Longer naps let you fall into deep sleep, so waking mid-cycle can leave you groggy, and napping late in the day can make it harder to fall asleep at night.
How much sleep do kids and older adults need?
Recommended hours drop with age — from 14–17 hours for newborns down to 7–9 hours for adults and 7–8 for older adults. See the age-by-age table above for the full CDC breakdown.