Bedtime By Sleep Cycles Calculator

Work out bedtime by sleep cycles instantly with clear inputs, formula shown and shareable results.

About Bedtime By Sleep Cycles Calculator

Sleep runs in cycles of roughly 90 minutes, and waking at the end of a cycle — in light sleep rather than deep sleep — feels far better than waking mid-cycle. Counting back whole cycles from the alarm, plus time to fall asleep, gives the bedtime to aim for.

Formula

Cycle-based bedtime

bedtime = wake time - (cycles x cycle length) - sleep latency

Worked example

With the default values below, Bedtime By Sleep Cycles Calculator returns Bedtime (24h clock) of 22.77. Change any input above and every figure here is recalculated in your browser.

Inputs used

Wake-up hour (24h): 6.5 h
Sleep cycles wanted: 5 cycles
Cycle length: 90 min
Time to fall asleep: 14 min

Results

Bedtime (24h clock): 22.77 h
Total sleep: 7.50 h
Time in bed: 7.73 h
Sleep with one cycle fewer: 6.00 h

Step by step

1Values used
2Cycle-based bedtime
3Bedtime (24h clock)= 22.77 h
4Total sleep= 7.50 h
5Time in bed= 7.73 h
6Sleep with one cycle fewer= 6.00 h

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is the cycle always 90 minutes?

It averages 90 but ranges from 70 to 120 minutes and lengthens through the night. Treat it as an approximation rather than a clock.

Is five cycles enough?

Five cycles is 7.5 hours, within the recommended range for most adults. Four cycles at six hours is a workable minimum but not sustainable long term.