Sleep Cycle Calculator

How This Calculator Works

A full night’s sleep is made up of a series of roughly 90-minute cycles, each moving through lighter and deeper stages of sleep. Waking up between cycles — rather than in the middle of a deep one — commonly correlates with feeling more rested, even at the same total sleep time. Enter either the time you want to wake up or the time you’re going to bed, and this calculator suggests several options that land on a whole number of cycles.

The Formula

$$\text{Sleep Time} = \vA{n} \times 90 \text{ minutes}$$

where $\vA{n}$ is the whole number of cycles (3, 4, 5, or 6). This calculator shows four options — 3, 4, 5, and 6 cycles (4.5, 6, 7.5, and 9 hours of sleep) — headlined by 5 cycles (7.5 hours), the most commonly cited target for a full night’s rest.

Worked Example

Wanting to wake up at 7:00 AM, for a 5-cycle (7.5-hour) night:

1. Sleep time needed: $\vA{5} \times 90 \text{ minutes} = 450 \text{ minutes}$ (7.5 hours).
2. Bedtime: $\text{7:00 AM} - \text{7.5 hours} = \text{11:30 PM}$ the night before.

A Note on Accuracy

The 90-minute cycle length is a commonly-cited average, not an exact figure for any individual — actual cycle length varies from person to person and night to night, and this calculator also doesn’t account for the time it typically takes to actually fall asleep after getting into bed (commonly estimated around 15 minutes) — plan to get into bed a little before the suggested bedtime to allow for that. Use these suggestions as a starting point to experiment with, not a precise prescription.