Sleep Calculator
Sleep Calculator works out Recommended time and Recommended time (12-hour clock) from Wake-up time, Time you get into bed and Target sleep length. The default figures on this page give recommended time of 23:15; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
6 steps
- Sleep cycle length 90 minutes, sleep-onset allowance 15 minutes.
- 6 cycles = 6 x 90 = 540 min asleep (9 h): bed 21:45, wake 07:00.
- 5 cycles = 5 x 90 = 450 min asleep (7.5 h): bed 23:15, wake 07:00.
- 4 cycles = 4 x 90 = 360 min asleep (6 h): bed 00:45, wake 07:00.
- 3 cycles = 3 x 90 = 270 min asleep (4.5 h): bed 02:15, wake 07:00.
- Adults 18 and over: 7-9 hours per 24 h. Watson NF et al., Sleep 2015;38:843-844: adults should sleep 7 or more hours per night.
All cycle-aligned optionstable
| cycles | bedTime | wakeTime | sleepHours | timeInBedHours |
|---|---|---|---|---|
| 6 | 21:45 | 07:00 | 9 | 9.25 |
| 5 | 23:15 | 07:00 | 7.5 | 7.75 |
| 4 | 00:45 | 07:00 | 6 | 6.25 |
| 3 | 02:15 | 07:00 | 4.5 | 4.75 |
Its 4 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
4 sources
What the Sleep Calculator calculates
Works out bedtimes or wake times that land at the end of a whole 90-minute sleep cycle, allowing for how long it takes to fall asleep, and checks the resulting sleep length against the age-appropriate recommendation.
How to use this Sleep Calculator
Enter Wake-up time, Time you get into bed, Target sleep length and Sleep cycle length. Recommended time updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Recommended time, Recommended time (12-hour clock) and Cycles in that option.
The method follows Carskadon MA & Dement WC, Normal Human Sleep: An Overview, in Kryger, Roth & Dement (eds), Principles and Practice of Sleep Medicine, Elsevier, Watson NF et al., Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society, Sleep 2015;38(6):843-844, Paruthi S et al., Recommended Amount of Sleep for Pediatric Populations: A Consensus Statement of the American Academy of Sleep Medicine, Journal of Clinical Sleep Medicine 2016;12(6):785-786 and Ohayon M et al., National Sleep Foundation’s sleep quality recommendations: first report, Sleep Health 2017;3(1):6-19.
Adult who must be up at 07:00 example
With What do you want to work out?: wake-at, Wake-up time: 07:00, Age: 30, the calculator returns Recommended time: 23:15, Cycles in that option: 5, Sleep in that option: 7.5. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Recommended time, Recommended time (12-hour clock) and Cycles in that option. The inputs you can vary are Wake-up time, Time you get into bed, Target sleep length, Sleep cycle length, Time it takes you to fall asleep and Age.
Understanding Recommended time, Recommended time (12-hour clock) and Cycles in that option
Sleep-cycle timing is a scheduling convenience, not a treatment. Cycle length varies between people and across the night, and waking "between cycles" has not been shown to change daytime alertness on its own. Persistent trouble falling asleep, staying asleep, loud snoring, or sleepiness despite adequate time in bed should be assessed by a clinician rather than rescheduled.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
How do I calculate how much sleep I actually need?
Works out bedtimes or wake times that land at the end of a whole 90-minute sleep cycle, allowing for how long it takes to fall asleep, and checks the resulting sleep length against the age-appropriate recommendation. Open “How this is worked out” beside the result to see each step for your own figures.
What is the 3-3-3 rule for sleep?
On the figures this page opens with — age 30 years — the recommended time is 23:15. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
What information do I need for the Sleep Calculator?
You need Wake-up time, Time you get into bed, Target sleep length, Sleep cycle length, Time it takes you to fall asleep, Age, Most cycles to show and Fewest cycles to show. The page opens with default figures that give recommended time of 23:15, so you can see the scale before entering your own.
What does this Sleep Calculator show?
It shows Recommended time, Recommended time (12-hour clock), Cycles in that option, Sleep in that option, Get into bed at, Wake at, Start winding down at and Time in bed, with the working and any warnings for your entries.
Can I check how the Sleep Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.