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Sleep Calculator
Step 1 of 10%
How it works
A complete sleep cycle (NREM 1→2→3→REM) lasts ~90 minutes. Waking during light NREM 1/2 feels easy; waking from deep NREM 3 or vivid REM feels groggy. Aiming for an integer number of cycles + sleep latency gets you near a light phase.
Worked example
Need to wake at 06:30:
- 4 cycles (6h): bed at 23:46
- 5 cycles (7.5h): bed at 22:16
- 6 cycles (9h): bed at 20:46
Who should use this
- •Anyone wanting better mornings
- •Shift workers planning naps
- •Teens needing structured sleep
- •Insomnia sufferers structuring routine
Common mistakes
- ×Trying to 'catch up' at weekends — disrupts circadian rhythm
- ×Long late naps (>30 min after 3pm) — wreck nighttime sleep
- ×Caffeine after lunch — half-life is 5-7 hours
- ×Doomscrolling in bed — blue light delays melatonin
Frequently asked questions
How long is a sleep cycle?▾
Roughly 90 minutes on average — varies between 80 and 110 minutes by individual.
Is 6 hours enough?▾
Most adults need 7-9. Six is the bare minimum and consistent sleep debt impairs performance, mood and immunity.
Why do I feel worse after 9 hours?▾
You may have woken mid-cycle. Try aligning to 7.5 or 9 hours from sleep onset.
Do sleep trackers know cycles?▾
Consumer wearables estimate cycles from heart-rate variability — directionally useful but not lab-grade accurate.