ZovaTool

Sleep Calculator

Go to bed at

21:456 cycles • 9 hrs
23:155 cycles • 7.5 hrs
00:454 cycles • 6 hrs
02:153 cycles • 4.5 hrs

How to use the Sleep Calculator

  1. Pick: I want to wake at X, or I'm going to bed at X.
  2. Enter the time.
  3. See the optimal bedtimes (or wake times) that align with full 90-minute REM cycles.
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Why sleep cycles matter

One sleep cycle ≈ 90 min: light → deep → REM. Waking mid-cycle (especially mid-deep) leaves you groggy.

Adults need 5–6 cycles (7.5–9 hours). The calculator adds 15 min for falling asleep.