ToolZone

Sleep Cycle Calculator

Calculate the ideal bedtime or wake-up time based on 90-minute sleep cycles, so you wake up at the end of a cycle instead of in the middle of one.

Go to bed at one of these times
9:45 PM
9.0 hours, 6 sleep cycles
Recommended
11:15 PM
7.5 hours, 5 sleep cycles
Recommended
12:45 AM
6.0 hours, 4 sleep cycles
2:15 AM
4.5 hours, 3 sleep cycles

A full sleep cycle is about 90 minutes, and waking up at the end of one, rather than in the middle, tends to feel less groggy. This adds a 15 minute estimate for the time it typically takes to fall asleep.

About the Sleep Cycle Calculator

A sleep cycle calculator works out the ideal bedtime or wake-up time based on 90-minute sleep cycles, so you're more likely to wake up at the end of a cycle rather than in the middle of one.

How to use

1

Choose whether you're setting a wake-up time or a bedtime.

2

Enter that time.

3

Pick one of the suggested times, aiming for 5 or 6 full sleep cycles for the most restorative rest.

Worked examples

Example: working backward from a wake-up time

Needing to wake up at 6:30 AM and wanting 5 full sleep cycles.

Input
6:30 AM minus (5 × 90 min) minus 15 min to fall asleep
Result
Ideal bedtime ≈ 10:15 PM

Frequently asked questions

Why does waking up mid-cycle feel worse than waking up at the end of one?
Sleep moves through distinct stages within each 90-minute cycle, and waking during deep sleep tends to cause grogginess, while waking near the end of a cycle, closer to lighter sleep, generally feels easier.
Is 90 minutes exactly right for everyone?
It's an average. Individual sleep cycle length varies somewhat from person to person, so treat these times as a helpful starting point rather than an exact science.

Explore more tools in the Calculators category.