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Sleep Calculator

Calculate the best time to sleep or wake up based on sleep cycles

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Includes 14 minutes average time to fall asleep

Best Bedtimes

Choose a time to wake up between sleep cycles for optimal rest:

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About Sleep Cycles

A complete sleep cycle lasts approximately 90 minutes and includes stages of light sleep (N1, N2), deep sleep (N3), and REM (dream) sleep. Waking at the end of a cycle, rather than in the middle, helps you feel more refreshed.

The average person takes about 14 minutes to fall asleep, which this calculator accounts for. For best results, aim for 5 or 6 complete cycles (7.5 or 9 hours of sleep).

Frequently Asked Questions

How many hours of sleep do I need?
Adults need 7-9 hours (4-6 sleep cycles of 90 minutes each). Teenagers need 8-10 hours, school-age children 9-12 hours.
What is a sleep cycle?
A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM sleep. Waking between cycles rather than during one helps you feel refreshed.
Why do I feel tired after 8 hours of sleep?
You may be waking in the middle of a sleep cycle (especially deep sleep). Try adjusting your bedtime by 15-30 minutes so you complete full 90-minute cycles.

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Read the SnoopTool guide behind this tool

The calculator gives you the number. These SnoopTool guides explain the method, the assumptions and the decision — with worked examples, data tables and FAQs.

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