Sleep Calculator

Free sleep cycle calculator. Find the best bedtime or wake-up time based on 90-minute sleep cycles for restful sleep.

How the Sleep Calculator works

A full sleep cycle lasts approximately 90 minutes, and waking at the end of a cycle feels more restful. The calculator counts backward from your target wake time in 90-minute intervals (plus a 15-minute falling-asleep buffer) to suggest optimal bedtimes.

Formula

Bedtime = Wake Time − (90 min × N cycles) − 15 min

How to use the Sleep Calculator

  1. 1The sleep calculator is designed to be simple and fast.
  2. 2Choose your mode: wake at a specific time or sleep now.
  3. 3Enter your desired wake-up time if applicable.
  4. 4See recommended bedtimes based on sleep cycles.
  5. 5Your result is shown immediately.

Examples

  • Wake at 7:00 AM = sleep at 11:45 PM (5 cycles)
  • Sleep now = wake in 7.5 hours for best result

Benefits

  • Completely free with no signup required.
  • Runs entirely in your browser for instant results and privacy.
  • Works on mobile, tablet and desktop.
  • Results can be copied with one click.

Frequently Asked Questions

Is the sleep calculator free to use?

Yes. The sleep calculator is 100% free, with no signup, no watermark and no hidden limits.

Does the sleep calculator store my data?

No. All calculations and processing happen locally in your browser. Nothing is uploaded to a server.

Does the sleep calculator work on mobile?

Yes. The sleep calculator is fully responsive and works on phones, tablets and desktop computers.

What is a sleep cycle?

A sleep cycle lasts about 90 minutes. Waking at the end of a cycle helps you feel refreshed. Most adults need 4-6 cycles (6-9 hours).

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