About the Sleep Calculator
Waking up in the middle of deep sleep is what makes you groggy. This sleep calculator works in 90-minute sleep cycles to suggest bedtimes — or wake-up times — that land at the end of a cycle.
Choose whether you know your wake-up time or your bedtime, enter it, and allow for the time you usually take to fall asleep.
How does the Sleep Calculator work?
A night’s sleep runs in cycles of roughly 90 minutes, each moving from light sleep through deep sleep to REM (dreaming) sleep. Waking at the end of a cycle, when sleep is lightest, usually feels easier than waking in the middle of one.
The suggested times give 6, 5, 4 or 3 full cycles — 9, 7.5, 6 or 4.5 hours — plus the minutes it takes you to fall asleep.
Sleep Calculator formula
bedtime = wake-up time − (cycles × 90 minutes) − time to fall asleepExample
To wake at 7:00 am with five cycles (7.5 hours) and 15 minutes to fall asleep, go to bed at 11:15 pm.
Tips
- Five or six cycles (7.5–9 hours) suits most adults; the five-cycle time is shown first.
- A regular wake-up time, even at weekends, does more for sleep quality than any calculator.
- Cycle length varies from person to person — if you wake tired, try shifting by 15 minutes.