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90-Minute Sleep Cycle & Optimal Bedtime Calculator

Calculate the ideal bedtime or wake-up time based on natural 90-minute REM sleep cycles and a 14-minute fall-asleep buffer.

If I need to wake up at 7:00 AM, what time should I go to sleep?If I go to bed right now, what are the best times to set my alarm?Why do 90-minute sleep cycles prevent waking up groggy?
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Sleep Planning Mode

Human sleep operates in natural 90-minute REM cycles. Waking up at the end of a cycle helps you feel alert, refreshed, and energized rather than groggy. Calculations include an average 14-minute fall-asleep buffer.

Suggested Bedtimes
Optimal 90-Min Sleep Windows

Choose one of the times below to complete whole sleep cycles.

21:46RECOMMENDED
9 hours of sleep (6 cycles)
Optimal / Well Rested (9.0 hrs)
23:16RECOMMENDED
7.5 hours of sleep (5 cycles)
Recommended (7.5 hrs)
00:46
6 hours of sleep (4 cycles)
Minimum (6.0 hrs)
02:16
4.5 hours of sleep (3 cycles)
Acceptable (Power)

How this calculation works

Calculates whole multiples of 90-minute REM cycles so you awaken during light sleep rather than deep sleep.

Formula
Optimal Time = Target Time ± (Number of Cycles × 90 min) ± 14 min Fall-Asleep Buffer

Frequently asked questions

7.5 hours corresponds to exactly 5 complete 90-minute sleep cycles. Waking up at 8 hours often interrupts deep Stage 3/4 sleep, causing sleep inertia and morning grogginess.

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Calculations run entirely in your browser. Your financial data is never sent to a server.

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