Sleep Calculator

Plan your sleep around sleep cycles

This sleep calculator suggests bedtimes or wake-up times that line up with full sleep cycles. Waking at the end of a cycle, rather than in the middle of one, may help you feel less groggy. Pick a time and the calculator lists four options with the hours of sleep each one gives you.

How to use it

1. Choose a mode: I want to wake at… or I want to sleep at….
2. Enter your wake-up time or your bedtime.
3. Read the list of suggested times for 6, 5, 4 and 3 sleep cycles. The 6-cycle option is marked Best.

How the calculation works

The calculator uses two fixed assumptions:

• One sleep cycle lasts 90 minutes.
• It takes 15 minutes to fall asleep.

Bedtime = wake-up time − (cycles × 90 minutes) − 15 minutes. In the other mode, wake-up time = bedtime + (cycles × 90 minutes) + 15 minutes.

Example: to wake at 7:00 AM after 5 cycles, go to bed 5 × 90 + 15 = 465 minutes (7 hours 45 minutes) earlier, at 11:15 PM.

Bedtimes for a 7:00 AM alarm

Cycles	Sleep time	Go to bed at
6	9 hours	9:45 PM
5	7.5 hours	11:15 PM
4	6 hours	12:45 AM
3	4.5 hours	2:15 AM

If you go to bed at 11:00 PM instead, the suggested wake-up times are 8:15 AM, 6:45 AM, 5:15 AM and 3:45 AM.

Tips for better sleep timing

• Most adults need at least 7 hours, so the 5- and 6-cycle options suit most people.
• If you usually fall asleep faster or slower than 15 minutes, shift the suggested time to match.
• Real cycles are not exactly 90 minutes for everyone, so treat the times as a guide.
• Keeping the same wake-up time every day matters more than hitting an exact cycle.

Frequently asked questions

How many hours of sleep does the calculator show?

It shows 9, 7.5, 6 and 4.5 hours of sleep, which are 6, 5, 4 and 3 full cycles. The 15 minutes to fall asleep is added on top.

Does it consider my age?

No. It uses the same 90-minute cycle and 15-minute fall-asleep time for everyone.

Is anything saved?

No. The times are calculated in your browser and nothing is stored.