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Sleep Cycle Calculator

Find the bedtime or wake time that ends with a complete 90-minute sleep cycle so you wake up feeling refreshed instead of groggy.

Your data never leaves your device
I want to
21:46
6 cycles · 9h sleep
Most refreshed
23:16
5 cycles · 7.5h sleep
00:46
4 cycles · 6h sleep
02:16
3 cycles · 4.5h sleep
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Frequently Asked Questions

  • Why 90-minute cycles?

    A typical adult sleep cycle averages 90 minutes through light, deep, and REM stages. Waking at the end of a cycle (rather than mid-cycle) avoids the heavy "sleep inertia" feeling.

  • What is the fall-asleep buffer?

    Average adults take 10–20 minutes to fall asleep. We default to 14 — adjust it to match your usual onset.

  • How many cycles should I aim for?

    5–6 cycles (7.5–9 hours) for most adults. 3–4 (4.5–6 hours) is short-term survival sleep, not a long-term plan.

  • Is anything tracked?

    No. The math runs in your browser. No times leave the page.