How the sleep cycle calculator works
Sleep happens in repeating cycles of roughly 90 minutes, each moving through light sleep, deep sleep and REM. Waking in the middle of a cycle leaves you groggy; waking at the end of one leaves you refreshed. This calculator adds (or subtracts) full 90-minute cycles plus a 15-minute buffer for falling asleep, so you wake at a natural break point.
How much sleep do you actually need?
Most adults need 7 to 9 hours — that's 5 to 6 full cycles. If you have to choose, a complete cycle beats more minutes: waking after 6 hours (4 cycles) can feel better than waking after 6.5 hours in the middle of deep sleep. For the full picture of how sleep stages fit together, see how sleep phases work.
The honest caveat
The 90-minute figure is an average, and your personal cycle length can differ. Use the calculator as a starting point, then let your own mornings tell you the truth. If you regularly wake groggy no matter the timing, the cause is often something else — snoring, pauses, or a fragmented night — which is worth a closer look.
See your actual cycles, not the average. SleepTrace records your night on your iPhone and maps your real sleep stages — no wearable. Download on the App Store →