Bedtime Calculator
The Bedtime Calculator computes bedtime from the relation bedtime hour = wake hour - (cycles x 90 + fall asleep minutes) / 60, wrapped to 24 hours. It takes 3 inputs (wake up time as 24 hour decimal (for example 6.5 is 6:30) in hours, number of 90 minute sleep cycles in cycles, time to fall asleep in minutes) and returns the bedtime. These tools are for pet owners and for anyone planning a day around the weather, their time outdoors, their sleep or their working hours, turning something you already know, a pet's age, a UV index, a bedtime or the length of a work session, into a figure you can act on. Enter your values below and the result updates instantly, and you can share a permalink that pre-fills the exact calculation. Enter your own actual figures rather than a typical or average value, check the units and the time format shown on each field before you read the answer, and run it again whenever your inputs change, because a result only holds for the conditions and the routine you entered. For example, with wake up time as 24 hour decimal (for example 6.5 is 6:30) = 7 hours, number of 90 minute sleep cycles = 6 cycles, time to fall asleep = 14 minutes, the bedtime works out to 21.766667, and the worked example further down the page shows every step so you can follow the arithmetic and reproduce it by hand. The method is the standard form documented by U.S. CDC, About Sleep, and the figure above each result carries the date it was last verified. The result describes a typical pattern rather than an individual: animals vary by breed, size and health, and people vary in how they tolerate sun, cold, lost sleep and long stretches of focus, so treat the figure as a planning guide and take any worry about an animal to a veterinarian, or about your own health to a qualified clinician.
With Wake up time as 24 hour decimal (for example 6.5 is 6:30) = 7 hours, Number of 90 minute sleep cycles = 6 cycles, Time to fall asleep = 14 minutes, the result is 21.766667.
Applies to: any numeric inputs. Method source: U.S. CDC, About Sleep, checked 2026-06-23.
The formula
bedtime hour = wake hour - (cycles x 90 + fall asleep minutes) / 60, wrapped to 24 hours
Worked example
With Wake up time as 24 hour decimal (for example 6.5 is 6:30) = 7 hours, Number of 90 minute sleep cycles = 6 cycles, Time to fall asleep = 14 minutes:
- Total sleep need = cycles x 90 + latency = 554 minutes
- Bedtime hour = wake hour - total minutes / 60, wrapped to 24 hours = 21.7667
- Bedtime = 21.766667
This worked example is one of the automated golden-value tests this calculator must pass before it can publish.
What this assumes
- Inputs are real numbers in the units shown.
- The result is the exact value of bedtime hour = wake hour - (cycles x 90 + fall asleep minutes) / 60, wrapped to 24 hours; general information, not professional advice.
Frequently asked questions
What formula does this use?
bedtime hour = wake hour - (cycles x 90 + fall asleep minutes) / 60, wrapped to 24 hours, the standard form documented by U.S. CDC, About Sleep.
Does the result ever change over time?
No. This is a pure formula with no external rate, so the same inputs always give the same result.
Official sources and verification
- Method: U.S. CDC, About Sleep, checked 2026-06-23.
Reviewed by the CalculatorHub team, edited by James Graham, 2026-06-23. See our methodology. General information, not professional advice.