Sleep happens in roughly 90-minute cycles, from light sleep down to deep sleep and back. Waking up in the middle of a cycle is what makes you feel groggy, even after eight hours in bed. Waking at the end of a cycle feels dramatically easier — that is why a 6-hour night can sometimes feel better than a 7.5-hour one that ends mid-cycle.
A sleep cycle calculator does the backwards math for you. Enter the time you need to get up, and it suggests bedtimes that land at the end of complete cycles, with about 14 minutes added for the average time it takes to fall asleep. Heading to bed right now? The “sleep now” mode works forwards instead, giving you wake-up times to choose from.
Find your ideal bedtime in 3 steps
- Open the faymox Sleep Cycle Calculator.
- Enter the time you need to wake up — or tap “Sleep now” if you are heading to bed.
- Pick one of the suggested bedtimes. Each one lands at the end of a full 90-minute cycle, so you wake up refreshed instead of groggy.
FAQ
How many sleep cycles do I need per night?
Most adults do well with 5 to 6 complete cycles, which is roughly 7.5 to 9 hours including time to fall asleep. Teenagers and athletes often need the upper end; sleep needs vary by person.
What if I cannot fall asleep in 14 minutes?
Fourteen minutes is an average. If you usually take longer, just go to bed a bit earlier than the suggested time — the cycle math still works, since it counts from when you actually fall asleep.
Does the calculator work for naps?
Yes. A 20-minute nap avoids deep sleep entirely, while a full 90-minute nap completes one cycle. The calculator's short-nap mode suggests both options.