Sleep Calculator
Wake up refreshed — find bedtimes and wake times aligned to 90-minute sleep cycles.
How to use
- Choose whether you're setting a wake-up time or a bedtime.
- Enter the time.
- Pick one of the suggested times to wake or sleep at the end of a full cycle.
How the Sleep Calculator works
Suggests bedtimes or wake times aligned to complete sleep cycles, so your alarm is less likely to land in the middle of deep sleep.
It assumes a 90-minute sleep cycle plus about 14 minutes to fall asleep, then works backwards or forwards from your chosen time to produce options at 6, 5, 4 and 3 complete cycles.
offset = cycles × 90 minutes + 14 minutes to fall asleep
Worked example
To wake at 7:00 AM, six full cycles means going to bed around 10:16 PM; five cycles gives 11:46 PM.
Things worth knowing
- Ninety minutes is an average. Real cycles range from roughly 70 to 120 minutes and change through the night, so treat these as approximations.
- Waking at the end of a cycle rather than mid-deep-sleep is what reduces grogginess — the effect is real but modest.
- Most adults need seven to nine hours. Five cycles is 7.5 hours and is the usual target; three cycles is a short-night fallback, not a plan.
Frequently asked questions
Why 90-minute cycles?
A full sleep cycle averages about 90 minutes; waking at the end of one helps you feel less groggy.
What's the 14 minutes for?
It assumes the average person takes around 14 minutes to fall asleep.
Is it better to get 6 hours or 6.5?
Six hours is four complete cycles and often feels better than waking mid-cycle at 6.5. Consistently short sleep still carries a cost regardless of timing.