Sleep Calculator
Calculate the best time to go to bed or wake up based on natural 90-minute sleep cycles, so you wake up feeling refreshed instead of groggy.
How to use the Sleep Calculator
- Choose whether you know your wake-up time or your bedtime.
- Enter the time.
- Adjust how many minutes you usually take to fall asleep (default 14).
- Click Calculate to see times for 3 to 6 sleep cycles.
Formula used
Worked example
Wake up at 6:30 AM, falling asleep in 15 minutes
6 cycles (9 h): go to bed at 9:15 PM
5 cycles (7.5 h): bed at 10:45 PM
4 cycles (6 h): bed at 12:15 AM
Why 90-minute cycles?
Sleep moves through light, deep and REM stages in cycles averaging about 90 minutes. Waking at the end of a cycle, rather than in deep sleep, usually feels less groggy. Most adults need 7–9 hours, which is 5 or 6 cycles; teenagers need more. Cycle length varies between 70 and 120 minutes, so use these times as a starting point and adjust by 15 minutes based on how you feel.
Tips for accurate results
- Keep the same wake-up time every day, including weekends.
- Avoid screens and caffeine late in the evening.
- If you regularly feel tired after 8 hours, speak to a doctor.
Frequently Asked Questions
7–9 hours for most adults.
About 10:15 PM (5 cycles) or 8:45 PM (6 cycles), allowing 15 minutes to fall asleep.
Not for most adults over the long term.
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Content reviewed by Vinod, Easy Smart Calculator · Last updated October 2026
Frequently Asked Questions
Why does sleep come in 90-minute cycles?
A full sleep cycle (light sleep, deep sleep, REM) lasts about 90 minutes. Waking up at the end of a cycle, rather than in the middle, helps you feel more refreshed.
How many sleep cycles should I aim for?
Most adults need 5-6 complete cycles per night, which equals about 7.5 to 9 hours of sleep.
Is this calculator medically accurate?
It's based on average sleep cycle research and provides a helpful estimate, but individual sleep patterns vary. Consult a doctor for chronic sleep issues.