Adults: 90 min. Children: 60. Some adults run 80–100.
Suggested bedtimes
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Most adults need 5–6 cycles (7.5–9 h). Choose the latest you can.
| Cycles | Time | Total sleep |
|---|
Nap-length recommender
| Nap type | Length | What you get |
|---|---|---|
| Power nap | 10–20 min | Alertness, no grogginess |
| Recovery nap | 30 min | Some sleep inertia, more rest |
| Slow-wave nap | 60 min | Memory boost, ~10 min grogginess |
| Full-cycle nap | 90 min | One full REM cycle, no grogginess |
How the math works
Sleep moves through ~90-minute cycles (light → deep → REM). Waking at the end of a cycle leaves you alert; mid-cycle (especially mid-deep-sleep) is what produces grogginess.
From a target wake time, the calculator subtracts 4, 5, 6, 7 cycles and adds fall-asleep latency. From a bedtime, it adds cycles after latency.