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Sleep Cycle Calculator

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

Suggested Bedtimes

9:45 PM6 cycles · 9.0h sleep
11:15 PM5 cycles · 7.5h sleep
12:45 AM4 cycles · 6.0h sleep
2:15 AM3 cycles · 4.5h sleep

Related Guide

Sleep Cycle Calculator: Why Waking Up Mid-Cycle Feels So Bad

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About This Tool

Free sleep cycle calculator online — enter either your desired wake-up time or bedtime, and instantly see the optimal times to fall asleep or wake up based on complete 90-minute sleep cycles. No sign-up, no upload, entirely browser-based. Sleep occurs in cycles of roughly 90 minutes, and waking up in the middle of a cycle (especially deep sleep) tends to cause grogginess, while waking up between cycles tends to feel more refreshing — even with the same total number of hours slept. This tool works backward or forward from your target time in 90-minute increments, plus a buffer for the average time it takes to fall asleep.

How to Use

  1. 1

    Choose a mode

    Select "I want to wake up at" or "I'm going to bed now."

  2. 2

    Enter your target time

    Input your desired wake-up time, or use the current time for bedtime mode.

  3. 3

    See your options

    View several bedtime or wake-up options, each aligned to a whole number of 90-minute sleep cycles.

Frequently Asked Questions

Why 90-minute cycles?+
A full sleep cycle — moving through light sleep, deep sleep, and REM sleep — takes approximately 90 minutes on average. Waking up at the end of a complete cycle, rather than in the middle of one, generally feels less groggy.
How many sleep cycles should I aim for?+
Five complete cycles (7.5 hours) is a common target for adults, though individual sleep needs vary. Some people feel best with 4 cycles (6 hours) while others need 6 (9 hours).
Does this account for the time it takes to fall asleep?+
Yes — the calculator adds an average falling-asleep buffer (typically around 15 minutes) before the first sleep cycle begins, so the suggested bedtime accounts for that transition period.

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