Sleep Cycle Calculator: Bedtimes and Wake-Up Times

How to use it

Choose whether you know your wake-up time or your bedtime.
Enter the Time in 24-hour form, for example 06:30.
Set Time to fall asleep. Keep 15 minutes unless you know it takes longer.
Read the Five-cycle time, then pick any row of the table that suits your day.

How the times are worked out

A sleep cycle moves through light sleep, deep sleep and dream sleep and lasts about 90 minutes on average. The Sleep Foundation says the first cycle of the night is often 70 to 100 minutes and later cycles run 90 to 120 minutes, and that a typical night has four to six cycles.

The Sleep Foundation also says a healthy adult usually takes 10 to 20 minutes to fall asleep. The calculator takes that time off the wake-up time, or adds it to the bedtime, then counts whole cycles of 90 minutes.

These times are a guide for planning and not medical advice. Cycles differ from person to person and from night to night. If you have trouble sleeping most nights, or you feel very sleepy in the day, see a doctor.

Bedtime    = wake-up time - time to fall asleep - (cycles x 90 min)
Wake-up    = bedtime + time to fall asleep + (cycles x 90 min)
Cycles     = 4, 5 or 6 (a typical night)

What the table does not show

How you feel on waking. Waking at the end of a cycle is a popular idea, but this tool does not measure it.
How much sleep you need. Some people need more than six hours in total, and the table shows only the cycles.
Sleep disorders, caffeine, shift work or medicines, which can change both the time to fall asleep and the cycles.

Worked example: waking at 07:00, 15 minutes to fall asleep

Six cycles of 90 minutes is 9 hours. Adding the 15 minutes to fall asleep, the bedtime is 07:00 - 15 minutes - 9 hours = 21:45.

Five cycles (7 h 30 min) give a bedtime of 23:15, and four cycles (6 h) give 00:45.

Cycles	Sleep	Bedtime
6	9 h 0 min	21:45
5	7 h 30 min	23:15
4	6 h 0 min	00:45

Frequently asked questions

Why are the cycles 90 minutes long?

The Sleep Foundation says a sleep cycle lasts about 90 minutes on average. The first cycle of the night is often shorter and later ones longer, so the times are a guide, not a fixed rule.

How long does it usually take to fall asleep?

The Sleep Foundation says a healthy adult usually takes 10 to 20 minutes. The calculator uses 15 minutes by default, and you can change it to match your own nights.

Does waking up at the end of a cycle help me feel rested?

It is a popular idea, but this calculator does not measure how rested you feel. It only gives times that fit complete cycles.

How much sleep do the rows add up to?

Four, five and six cycles of 90 minutes are 6, 7 hours 30 minutes and 9 hours. Your own need may be more or less than these totals.

What if I lie awake for hours most nights?

See a doctor. Long periods of being awake, or being very sleepy in the day, can have causes that a calculator cannot judge.

Are my times stored or sent to a server?

No. The times are calculated in your browser and nothing you enter is sent to us.

Sources

Figures and text last checked on Tuesday, November 10, 2026.

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