Sleep Cycle Calculator
Find the best time to sleep or wake up.
How to use
- 1 Choose whether you are starting from a wake-up time or a bedtime.
- 2 Enter the time using the picker.
- 3 Read the list of suggested times, ordered from most to least sleep.
- 4 Pick the option that fits your schedule and set your alarm.
About Sleep Cycle Calculator
The Sleep Cycle Calculator helps you wake up feeling refreshed instead of groggy by timing your sleep around complete 90-minute cycles.
Through the night your brain moves through light sleep, deep sleep and REM in roughly 90-minute loops; waking in the middle of a deep stage is what leaves you foggy, while waking at the boundary between cycles feels far more natural.
Tell the tool when you need to wake up and it works backwards to show several good bedtimes, each ending on a clean cycle boundary.
Or flip it around: tell it when you are going to bed and it lists the moments you should set your alarm for.
The calculation also adds a sensible buffer of about fifteen minutes for the time it actually takes to drift off, so the numbers reflect real life rather than the instant your head touches the pillow.
Options are ordered from the longest, most rested night down to the shortest viable one, so you can pick the best choice your schedule allows.
Adults generally do well on five to six cycles, which is roughly seven and a half to nine hours of sleep.
Everything is computed locally in your browser with no accounts, tracking or uploads, so you can plan tonight in a couple of taps and keep your routine entirely private.
FAQ
Why 90-minute cycles?
A full sleep cycle averages about 90 minutes across light, deep and REM stages. Waking at the end of a cycle, rather than mid-cycle, tends to feel far less groggy.
Does it account for the time it takes to fall asleep?
Yes. The calculator adds roughly 15 minutes for falling asleep, so the suggested times reflect when you should actually be in bed rather than already unconscious.
How many cycles should I aim for?
Most adults feel best with five to six complete cycles, which is about 7.5 to 9 hours. The tool lists longer options first so you can choose the most rest your schedule allows.