Sleep Cycle Calculator
Find bedtimes and wake times that line up with full 90-minute sleep cycles.
Bedtimes that complete full 90-minute cycles (with 15-min buffer to fall asleep). Top option is most rested.
Go to bed at
9:45 PM
6 cycles
9.0 hr sleep
Go to bed at
11:15 PM
5 cycles
7.5 hr sleep
Go to bed at
12:45 AM
4 cycles
6.0 hr sleep
Go to bed at
2:15 AM
3 cycles
4.5 hr sleep
About this tool
Waking up mid-cycle leaves you groggy. Waking up between cycles feels much better. This calculator works in both directions: tell it when you want to wake up, and it shows you bedtimes that complete full 90-minute cycles. Or tell it you're going to bed now, and it suggests wake times.
How to use it
- Pick a mode: 'I want to wake up at...' or 'I'm going to bed now'.
- If choosing a wake time, enter it. If going to bed now, the calculator uses the current time.
- We add a 15-minute buffer for falling asleep, then show 5 suggested times that line up with full sleep cycles.
FAQ
Why 90 minutes?+
A full sleep cycle (light → deep → REM → light) takes roughly 90 minutes for most adults. Waking at the end of a cycle, in light sleep, feels much better than waking mid-cycle in deep or REM sleep.
Why the 15-minute buffer?+
The average person takes 10–20 minutes to actually fall asleep after going to bed. A 15-minute buffer is a reasonable middle estimate.
How many cycles do I need?+
5–6 cycles (7.5 to 9 hours) is the sweet spot for most adults. 4 cycles (6 hours) works for some people but most will be tired. 3 cycles is a stopgap, not a sustainable plan.