Sleep Cycle Calculator

How to use the sleep cycle calculator

1. Choose The time I need to wake up to get bedtimes, or The time I will go to bed to get wake-up times.
2. Enter the time. Then set minutes to fall asleep, the time between lying down and actually sleeping. The starting value of 15 is only an example; change it to match you.
3. Read the table. Each row gives a time, the number of 90-minute cycles and the total sleep length. Choosing a time that ends a whole cycle is the idea behind this rule of thumb.
4. Press Use the current time as bedtime for a quick "if I go to bed now" answer, or Copy result to copy the table.

Formula

Times wrap around midnight. Cycles shown are 3, 4, 5 and 6, which is 4 hours 30 minutes to 9 hours of sleep.

Worked example

What this calculator is and is not

The idea is simple: sleep is often described as moving through repeating cycles that last about 90 minutes on average, so some people prefer to wake near the end of a cycle. The calculator does only that arithmetic. It is a rule of thumb. It does not measure your sleep, does not know your own cycle length, which varies between people and from night to night, and does not tell you how much sleep you need.

It is not medical advice. How long you should sleep depends on your age, health and circumstances. If you often feel unrested, have trouble falling or staying asleep, snore loudly or feel very sleepy in the day, talk with a doctor or other health professional instead of relying on a calculator.

Using the fall-asleep time well

People differ a lot in how long it takes to fall asleep, so the fall-asleep field accepts any whole number of minutes from 0 to 120. If you do not know your own number, watch the clock on a few ordinary nights and use the typical value you see. Each minute you add moves every bedtime one minute earlier.

You can also use the results as a starting menu. If the bedtime for six cycles is too early, look at five cycles and think about whether the shorter night is acceptable for you. When an alarm is fixed, such as for work or a flight, compute from the wake-up time. When the day is flexible, compute from the time you are going to bed.

To plan other parts of the day, see the time calculator for adding and subtracting hours, the time duration calculator for the length between two times, and the water intake calculator for an unrelated everyday estimate.

Privacy

The times you enter are used only in this page to do the arithmetic. Nothing is saved or sent anywhere. The "current time" button reads your device clock once when you press it.

Assumptions and limits

• A cycle is counted as exactly 90 minutes, which is an average and not a measurement of your sleep.
• The tool assumes you fall asleep after the number of minutes you enter and then sleep in whole cycles without waking.
• It does not account for naps, shift work, sleep disorders, medications, caffeine or alcohol.
• It is not medical advice and cannot diagnose or treat any sleep problem.
• Times are shown in 12-hour style with AM and PM and wrap around midnight. Time zones and daylight saving changes are not modeled.

Formulas reviewed October 10, 2026. See the calculation methodology for how SumPanda rounds, tests and sources its formulas.

Frequently asked questions