Sleep Cycle Calculator
Calculate ideal sleep or wake times based on 90-minute sleep cycles. Waking at the end of a cycle (not in the middle) leaves you feeling more refreshed.
Inputs
About Sleep Cycle Calculator
Sleep cycles
A full cycle averages ~90 minutes and progresses through light sleep → deep sleep → REM. Waking at the END of a cycle (vs being woken mid-deep-sleep) leaves you less groggy.
The fall-asleep buffer
Most people take 10-20 minutes to fall asleep, so the slider starts at 15 minutes and moves anywhere from 5 to 45. Whatever you set is added before the cycles are counted, so every time on the page shifts with it — no mental arithmetic needed.
Going to bed right now
Tap the “I’m going to bed NOW” button and the calculator switches to bedtime mode, reads the current clock time, and shows the wake times that land at the end of a full cycle.
Caveats
Cycle length varies 80-110 min by person and over the night. This is a rough guide — not strict science. Consistent bedtime/waketime matters more than micro-optimizing the wake moment.