Sleep calculator
Sleep runs in cycles of about 90 minutes, and waking at the end of a cycle rather than mid-cycle tends to feel less groggy. To wake at 7am, common bedtimes are about 9.46pm, 11.16pm or 12.46am, which give five or six complete cycles after roughly 14 minutes to fall asleep. Enter your wake-up time, or choose to sleep now, and the calculator shows the times that land you at the end of a cycle. These are planning figures, not a medical measurement.
Pick whether you want to set a wake-up time, set a bedtime, or sleep right now. The calculator allows about 14 minutes to drift off, then counts back or forward in 90-minute blocks so you wake between cycles.
How this is worked out
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to feel less groggy.
cycle length = 90 minutes
fall-asleep allowance = 14 minutes
bedtime = wake time − (cycles × 90 minutes) − 14 minutes
we show the options for 6, 5 and 4 complete cycles (about 9, 7.5 and 6 hours of sleep)
The 90-minute cycle and the 14-minute average time to fall asleep are widely used planning figures, not a medical measurement: real sleep varies by person and night. This is general information, not medical advice.
Looking for other time tools? Try the full set of calculators or the time-zone meeting planner.
The 90-minute sleep cycle and the average time to fall asleep are widely used planning figures. This is general information, not medical advice.
Common questions
How does the sleep calculator work?
It counts sleep in blocks of about 90 minutes and allows roughly 14 minutes to fall asleep, then works back from your wake-up time, or forward from now, so you wake at the end of a cycle rather than in the middle of one.
Why does the calculator use 90-minute cycles?
A full sleep cycle lasts about 90 minutes on average, moving through light, deep and REM sleep. Waking at the end of a cycle rather than in deep sleep tends to feel less groggy, which is why the calculator targets multiples of 90 minutes.
How many sleep cycles should I aim for?
Most adults do well on five or six complete cycles a night, roughly 7.5 to 9 hours of sleep. The calculator shows options for six, five and four cycles so you can pick what fits the time you have available.
Is this medical advice?
No. The 90-minute cycle and the 14-minute time to fall asleep are widely used planning figures, not a measurement of your own sleep, which varies by person and night. This is general information, not medical advice.
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Editor, Dates & Times
Oliver Mackman is the named editor of Dates & Times and a director of Best Business Loans Ltd (Companies House 16833937), the company that operates the site. He is accountable for its editorial standards, sourcing and corrections, and requires every result to cite the underlying date maths and the official UK source behind it, such as the gov.uk Bank Holidays API.
Last reviewed: 12 June 2026