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Health & Fitness

Sleep Cycle & Wake-Up Time Calculator

Work backward from your alarm, or forward from your bedtime, to land on a wake-up time aligned with full 90-minute sleep cycles.

What this does: calculates bedtime or wake-up time options spaced in complete 90-minute sleep cycles, plus a 15-minute average time-to-fall-asleep buffer, so you're more likely to wake up at the end of a cycle instead of in the middle of one. Runs entirely in your browser — no signup, nothing is uploaded.

Frequently asked questions

How does this sleep cycle calculator work?

It adds a 15-minute average time-to-fall-asleep buffer to whole 90-minute sleep cycles. Enter a wake-up time to see bedtimes counted backward in 3 to 6 full cycles, or enter a bedtime to see wake-up times counted forward, so you wake up at the end of a cycle rather than in the middle of one.

Why are sleep cycles based on 90 minutes?

A full sleep cycle, moving through light sleep, deep sleep and REM sleep, averages about 90 minutes in adults, though it can range from roughly 70 to 120 minutes depending on the person. Waking up between cycles rather than mid-cycle tends to reduce grogginess, known as sleep inertia.

How many sleep cycles should I get per night?

Most adults feel best after 5 to 6 full cycles, roughly 7.5 to 9 hours, per night. This calculator shows 3 to 6 cycles so you can compare options, but individual sleep needs vary, so use the results as a starting point rather than a fixed rule.