“Sleep now”: enter the time you plan to get into bed.
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Each sleep cycle is 90 minutes; a 15-minute sleep-onset latency is included. Aim for 4–6 cycles (6–9 hours).
| Cycles | Sleep duration | Wake time |
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How the 90-minute sleep cycle works
While you sleep, your brain passes through a repeating cycle of stages that lasts roughly 90 minutes on average. Each cycle moves from light sleep into deep (slow-wave) sleep and then into REM sleep, the stage where most dreaming happens. After REM, the cycle starts again, and a typical night contains four to six of these cycles.
Waking in the middle of deep sleep is what leaves you feeling groggy and disoriented. By timing your alarm to land near the end of a cycle — when sleep is naturally lightest — you are far more likely to wake up clear-headed. That is the idea behind this calculator: it adds complete 90-minute cycles (plus a little time to fall asleep) to find wake-up times that line up with the natural rhythm.
The wake-up times calculator works forward from your bedtime, while the bedtime calculator works backward from the time you need to get up. If you only have a short break, check the nap guide for 20, 30, 45 and 90-minute naps.
Remember that this is a general guide: individual cycle length varies (roughly 80–110 minutes), and factors like caffeine, stress and sleep debt can shift it. Use these times as a starting point, and let your own energy levels be the final judge.