Sleep Calculator
Work out a bedtime from the time you need to wake, or a wake-up time from when you go to bed, using your own cycle length and time to fall asleep.
Result
Enter length of one sleep cycle, in minutes, time to fall asleep, in minutes and number of cycles to see the result.
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How to use the Sleep Calculator
- Choose whether you know your wake-up time or your bedtime, and enter it.
- Enter the length of one of your sleep cycles in minutes, how long you usually take to fall asleep, and how many cycles you want to plan for.
- Read the bedtime or wake-up time, and whether it falls on the day before, the same day or the next day.
How the times are worked out
The page counts back from your wake-up time, or forward from your bedtime, by the whole number of cycles you chose plus the time it takes you to fall asleep:
time asleep = cycles × cycle lengthtime in bed = time asleep + time to fall asleepbedtime = wake-up time − time in bedwake-up = bedtime + time in bedThe answer wraps around midnight, and the day line says whether it falls on the day before, the same day or the next day. A long plan can cross two midnights, and the day line then says two days before or two days later. Every figure is in whole minutes, so the answer is always on the minute. Nothing on this page reads your device’s clock: the time you enter is the only time it uses.
Why every figure is yours
A sleep calculator is only as good as the numbers in it. The length of a cycle, how quickly you fall asleep and how many cycles you need all differ from person to person, and from night to night. So the page fills in none of them. It does the clock arithmetic exactly and leaves the assumptions to you, where you can see and change them.
If you are trying this for the first time, compare two or three versions: change the number of cycles by one, or the cycle length by ten minutes, and see how far the bedtime moves. That shows how much the result depends on the assumptions rather than on the arithmetic.
What this is not
This is a planning tool for a clock time. It does not measure sleep, diagnose a sleep problem or tell you how much sleep you need. Persistent trouble falling or staying asleep, or daytime sleepiness that does not improve with more time in bed, is worth discussing with a doctor.
With your numbers
- 5 cycles × 100 minutes = 8:20:00 asleep
- Adding 20 minutes to fall asleep gives 8:40:00 in bed
- 7:00 AM minus that is 10:20 PM, the day before
Quick reference
Uses the figures you enter. Real cycles vary in length through the night and from night to night.
| Example | Result |
|---|---|
| Wake 06:00, 90-minute cycles, 15 minutes, 5 cycles | Go to bed at: 10:15 PM |
| Wake 06:30, 90-minute cycles, 15 minutes, 5 cycles | Go to bed at: 10:45 PM |
| Wake 07:00, 100-minute cycles, 20 minutes, 5 cycles | Go to bed at: 10:20 PM |
| Wake 07:30, 110-minute cycles, 10 minutes, 4 cycles | Go to bed at: 12:00 AM |
| Bed 22:30, 90-minute cycles, 15 minutes, 5 cycles | Wake up at: 6:15 AM |
| Bed 23:30, 100-minute cycles, 20 minutes, 4 cycles | Wake up at: 6:30 AM |
Common questions about the Sleep Calculator
- Why does the page not fill in a cycle length?
- Because there is no single right figure. Sleep cycles run from light sleep through deep sleep to REM sleep and back, and descriptions of how long that takes give ranges rather than one number. Cycles also tend to change in length and make-up through the night. A default would look like a fact about your sleep when it is only a guess, so the page asks for your own figure.
- How can I find my own cycle length?
- A sleep study measures it directly. Some wearable devices estimate it, with less certainty. Without either, you can experiment: pick a figure, use it for a week or two, and adjust it by five or ten minutes if you often wake up groggy in the middle of the planned time.
- How many hours of sleep should I get?
- This page does not say, and does not suggest a number of cycles. How much sleep a person needs varies with age, health and circumstances. If you are regularly tired despite enough time in bed, or you snore heavily or stop breathing in your sleep, that is something to raise with a doctor rather than a calculator.
- What is the time to fall asleep for?
- The first cycle does not start the moment you lie down. Adding the minutes you usually spend awake in bed moves the bedtime earlier, or the wake-up time later, so that the cycles themselves are whole. Enter 0 if you fall asleep almost at once or want to leave it out.
- Does waking at the end of a cycle really help?
- The idea is that waking from light sleep feels easier than waking from deep sleep. Because real cycles drift in length, a plan built from an average can still land part-way through a cycle. Treat the result as a starting point for your own routine, not a guarantee.