Sleep Calculator: Best Bedtime and Wake-Up Time

Enter the time you need to wake up, or the time you are going to bed. The calculator lists times that line up with the end of a full sleep cycle, so you are less likely to wake partway through one.

How to use the sleep calculator

Choose whether you have a fixed wake-up time or a fixed bedtime, then type the time in 24-hour format (07:00 for 7 am, 23:30 for 11:30 pm). Adjust how long you usually take to fall asleep and, if you know it, your typical cycle length.

The highlighted result is for five full cycles, which is about 7.5 hours with the default settings. The list also shows 6, 4 and 3 cycles so you can choose what fits your evening.

The formula

Sleep runs in repeating cycles of light, deep and REM sleep, each lasting roughly 90 minutes. Waking at the end of a cycle usually feels easier than waking from deep sleep.

Bedtime = wake-up time − time to fall asleep − (number of cycles × cycle length). Wake-up time = bedtime + time to fall asleep + (number of cycles × cycle length). Times that cross midnight wrap around to the previous or next day.

Worked example

You need to be up at 07:00 and usually fall asleep in 15 minutes. Five cycles of 90 minutes is 450 minutes. Add 15 minutes and you get 465 minutes, or 7 hours 45 minutes. Counting back from 7:00 AM gives a bedtime of 11:15 PM.

Six cycles gives 9:45 PM, four cycles gives 12:45 AM and three cycles gives 2:15 AM.

Practical tips

Cycle length varies between people and through the night, so treat these times as estimates, not exact targets. If you often wake just before your alarm, your cycles may be shorter; try 85 minutes.

Most adults need 7 to 9 hours, so five or six cycles is the usual aim. A consistent schedule matters more than hitting a cycle to the minute. This tool gives general information, not medical advice.

Frequently asked questions

How long is one sleep cycle?

On average about 90 minutes, though it ranges from roughly 70 to 120 minutes depending on the person and the time of night.

Is it better to sleep 6 hours or 7 hours?

Six hours is four full cycles and 7.5 hours is five. Waking between cycles can feel better in the moment, but most adults need more total sleep than six hours for good health.

Why does the calculator add time to fall asleep?

Cycles start when you actually fall asleep, not when you get into bed. Adding 10 to 20 minutes makes the times more realistic.

What if I wake up in the night?

Brief awakenings are normal and the times are estimates. Use the results as a guide and adjust based on how you feel.