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Sleep Calculator

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

h
min
min

Results

6 cycles (9h) — Best21:-15
5 cycles (7.5h) — Good23:-45
4 cycles (6h) — Minimum00:45
Recommended Cycles5-6 cycles recommended
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What is Sleep?

Sleep occurs in 90-minute cycles, each consisting of light sleep, deep sleep, and REM sleep. Waking up between cycles (not during deep sleep) helps you feel refreshed rather than groggy.

Adults need 7-9 hours of sleep (5-6 complete cycles). This calculator works backward from your desired wake time to find the optimal bedtime.

Formula

Each sleep cycle = 90 minutes

6 cycles = 9 hours (ideal) 5 cycles = 7.5 hours (recommended) 4 cycles = 6 hours (minimum)

Bedtime = Wake Time − (Cycles × 90 min) − Time to Fall Asleep

How to use this Sleep Calculator?

1. Enter your desired wake-up time. 2. Enter how long it takes you to fall asleep (average 15 min). 3. See optimal bedtimes for 4, 5, and 6 sleep cycles.

Frequently asked questions

Why do I feel tired after 8 hours of sleep?
You may be waking up during deep sleep. Try waking up at 7.5 hours (5 cycles) or 9 hours (6 cycles) instead of 8 hours.
How many sleep cycles do I need?
Adults need 5-6 cycles (7.5-9 hours). Teens need 6-7 cycles. Older adults may need only 4-5 cycles.
What is the best time to sleep?
Between 9 PM and midnight is ideal because it aligns with your circadian rhythm and maximizes deep sleep in the first half of the night.
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