Sleep Calculator
Bedtimes that end on a full cycle.
Runs in your browserRelated
About
Sleep Calculator works backward or forward from a wake-up time, bedtime, or "right now" to find times that land at the end of a full 90-minute sleep cycle — the idea being that waking up between cycles feels far less groggy than waking up mid-cycle. It shows options from 1 to 6 cycles, highlights the 5- and 6-cycle options as recommended, and accounts for the time it typically takes to actually fall asleep. Each result links straight to a Timer preset. Cycle length and fall-asleep time are both adjustable. Runs entirely in your browser.
Frequently asked
- Why 90-minute cycles specifically?
- 90 minutes is the commonly cited average length of one full sleep cycle; the calculator lets you adjust it from 80 to 110 minutes if yours runs differently.
- Why are 5 and 6 cycles marked recommended?
- 5–6 cycles (about 7.5–9 hours) covers the commonly recommended sleep duration for adults; 1–2 cycles are marked short since that's a nap, not a night's sleep.
- Does it account for the time it takes to fall asleep?
- Yes, there's an adjustable "time to fall asleep" offset (14 minutes by default) applied on top of the cycle math.