Sleep cycle calculator: when to go to bed or wake up
Sleep runs in cycles. On average a cycle lasts about 90 minutes, but across people and nights it ranges from about 70 to 150. The calculator adds 4–6 cycles plus time to fall asleep and shows handy clock times. It is a rough guide, not an exact calculation. Nothing is stored.
Nothing is stored or sent: everything runs in your browser, even offline after the first visit.
What to do now
- Choose: you need to wake at a set time, or you are going to bed.
- Enter the time and how many minutes you usually take to fall asleep.
- Pick a time that suits you and go to bed a few minutes before it.
- Try it for three or four days and notice how you feel.
What not to do
- Do not lie watching the clock and counting minutes.
- Do not take the numbers as exact: your cycle may differ.
- Do not cut sleep to four cycles every night.
- Do not blame yourself if you did not fall asleep on schedule.
After the calculation
- Wake up at about the same time, weekends included.
- If mornings feel better, keep this schedule.
- If you take long to fall asleep, look at the sleep window and the article on night waking.
When to see a professional
- You take a long time to fall asleep or wake often at night.
- You feel very sleepy in the day even after enough sleep.
- Snoring with pauses in breathing, seizures or sleepwalking.
- Poor sleep lasts for weeks and gets in the way of life.
How it works
During sleep the brain moves through several stages, and they repeat in loops. One loop is called a cycle. On average it lasts about 90 minutes, and studies of healthy adults find much shorter and longer cycles too.
The calculator takes the cycle length (90 minutes by default), multiplies it by 4, 5 or 6 and adds time to fall asleep. That gives a few clock times. Pick the one that fits your schedule and gives 7–9 hours of sleep.
The model is simplified. It cannot see your sleep and does not know which stage you will wake in. If mornings are hard and you take long to fall asleep, shifting by 15 minutes changes little. Then it is better to look at your routine as a whole.
Sources
- Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health 2015;1(1):40–43
- Ohayon MM, Carskadon MA, Guilleminault C, Vitiello MV. Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep 2004;27(7):1255–1273
- Kishi A, Van Dongen HPA. Phenotypic interindividual differences in the dynamic structure of sleep in healthy young adults. Nat Sci Sleep 2023;15:465–476