Sleep Calculator

How this sleep calculator works

Waking up in the middle of a sleep cycle tends to leave you groggy, while waking up between cycles feels easier. This sleep cycle calculator, which also works as a bedtime calculator, lines up your bedtime or alarm with the end of a cycle. Pick whether you know when you need to wake up or when you are going to bed, enter that time, and it lists the matching times for one to seven full cycles.

Bedtime = wake-up time − time to fall asleep − cycles × cycle length
Wake-up time = bedtime + time to fall asleep + cycles × cycle length

The defaults are a 90-minute cycle and 15 minutes to fall asleep. Change either one if you know your own numbers. Times with five or six cycles are marked as recommended because they give 7.5 to 9 hours of sleep with the default cycle.

Planning by hours of sleep instead

If you would rather aim for a set amount of sleep, use the hours of sleep tab. It simply adds your sleep length to your bedtime, or subtracts it from your wake-up time. It does not add time to fall asleep, so get into bed a little earlier than the bedtime it shows.

What is a sleep cycle?

During the night you move back and forth between non-REM sleep, which includes deep sleep, and REM sleep, when most dreaming happens. One pass through both is a sleep cycle. According to the National Heart, Lung, and Blood Institute, the cycle starts over every 80 to 100 minutes, and there are usually four to six cycles a night. The 90-minute default sits in the middle of that range.

How much sleep do I need?

Experts recommend that adults sleep between 7 and 9 hours a night. Adults who regularly sleep less than 7 hours may have more health issues than those who sleep 7 or more. Children and teenagers need more sleep than adults, and the amount goes down as they get older.

Frequently asked questions

What time should I go to bed to wake up at 6 AM?

With 90-minute cycles and 15 minutes to fall asleep, go to bed at 8:45 PM for six cycles (9 hours of sleep) or 10:15 PM for five cycles (7.5 hours). If you can only manage four cycles, 11:45 PM still wakes you between cycles.

If I go to bed at 11 PM, when should I wake up?

Using the same defaults, set your alarm for 6:45 AM (five cycles) or 8:15 AM (six cycles).

What time should I wake up?

Aim for the end of a cycle. Start from when you go to bed, add the time it takes you to fall asleep, then add 90 minutes per cycle. Choose "Go to bed at" above to get the times. For a 10:30 PM bedtime, that is 6:15 AM (five cycles) or 7:45 AM (six cycles).

How long is one sleep cycle?

Roughly 80 to 100 minutes, and it varies from person to person and across the night. If you often wake up naturally a little before or after the suggested times, adjust the cycle length to match.

Does this work as a nap calculator?

Yes. Choose "Go to bed at", enter when you will lie down, and use the one-cycle time for a full-cycle nap.

Limitations

Sleep cycles are not exactly the same length for everyone or from one cycle to the next, so these times are estimates, not a guarantee of waking up refreshed. The calculator does not track your actual sleep stages, and it is not medical advice. Talk to a doctor if you regularly have trouble sleeping or feel tired during the day.