😴 Sleep Calculator

About this Sleep Calculator

Sleep Calculator works backwards (or forwards) from the way sleep actually works: in roughly 90-minute cycles of light and deep sleep. Waking at the end of a complete cycle feels far easier than being dragged out of deep sleep mid-cycle, so the tool suggests times that give you 4, 5 or 6 full cycles, plus about 15 minutes to drift off.

How to use it

1. To plan tonight: enter the time you must wake up and press the first button for bedtime options.
2. To plan tomorrow: enter your bedtime and press the second button for alarm options.
3. Pick the suggestion that gives you 7.5–9 hours where possible.
4. Keep the same wake time daily for the strongest effect.

Example

If you must wake at 7:00 AM, the calculator suggests bedtimes of 9:45 PM (9 hrs) or 11:15 PM (7.5 hrs).

Frequently asked questions

Why 90 minutes?

One full sleep cycle — light sleep, deep sleep and dreaming — averages about 90 minutes, though it varies a little between people.

What if I feel groggy even after 8 hours?

8 hours lands mid-cycle for many people. Try the 7.5 or 9 hour option and keep a consistent wake time for a week.

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