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Calculation Machine

Sleep Calculator

Best bedtimes and wake times by sleep cycle.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
6 cycles (9 hrs)
Sleep at 21:15
5 cycles (7.5 hrs)
Sleep at 22:45
4 cycles (6 hrs)
Sleep at 00:15
Recommended for adults
5–6 cycles, 7.5–9 hours
Falling-asleep buffer
15 minutes

Quick answer

Sleep runs in roughly 90-minute cycles, so waking at a multiple of 90 minutes after falling asleep feels far less groggy.

Worked example

Worked example

Using the values the calculator loads with.

Inputs

  • Wake-up time06:30 HH:MM
  • Minutes to fall asleep15

Result

  • 6 cycles (9 hrs)Sleep at 21:15
  • 5 cycles (7.5 hrs)Sleep at 22:45
  • 4 cycles (6 hrs)Sleep at 00:15
  • Recommended for adults5–6 cycles, 7.5–9 hours
  • Falling-asleep buffer15 minutes

How to use the Sleep Calculator

  1. 1Enter the time you must wake up.
  2. 2Set how long you usually take to fall asleep.
  3. 3Pick one of the suggested bedtimes.

Frequently asked questions

Why 90 minutes?

A full cycle through light, deep and REM sleep averages 90 minutes. Waking mid-deep-sleep causes grogginess.

Is 6 hours enough?

For most adults no — four cycles is a minimum for a short night, but 7–9 hours is the healthy range.

About this calculator