Fitness

Sleep cycle calculator

Calculate the best bedtime or wake-up time based on 90-minute sleep cycles.

Wake-up time

Cycles to show

Suggested bedtimes

Times include ~15 minutes to fall asleep. Adjust if you fall asleep faster or slower.

100% private. All processing happens locally in your browser — no files or data are ever sent to a server.

How to use Sleep cycle calculator

01 Fill in the required values using the fields provided
02 Results calculate automatically as you type
03 Copy or note the result — all calculations stay on your device

Frequently asked questions

Common questions about Sleep cycle calculator.

Is Sleep cycle calculator free to use?

Yes, Sleep cycle calculator is completely free. No account, subscription, or payment is ever required — just open the page and start using it.

Does Sleep cycle calculator upload my data to a server?

No. Sleep cycle calculator runs entirely in your web browser using client-side JavaScript. Your files, text, and data never leave your device, making it 100% private.

Can I use Sleep cycle calculator on my phone or tablet?

Yes. Sleep cycle calculator is fully responsive and works on all modern smartphones, tablets, and desktop browsers without installing any app.

Are these results accurate enough to rely on?

Sleep cycle calculator uses well-established formulas and provides accurate estimates for everyday use. For financial, medical, or legal decisions, always consult a qualified professional.

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About Sleep cycle calculator

Sleep occurs in cycles of approximately 90 minutes, alternating between lighter and deeper stages including REM (rapid eye movement) sleep. Waking in the middle of a deep sleep stage causes the grogginess known as sleep inertia — while waking at the end of a cycle, during a lighter stage, feels much more natural. The Sleep Cycle Calculator calculates the optimal times to wake up or fall asleep by counting backwards or forwards in 90-minute blocks. It adds a 15-minute window to fall asleep, so the times shown are when to get into bed, not when sleep actually begins.