Calculator
Sleep Duration Calculator
Work backwards from your wake-up time through 90-minute sleep cycles to find sensible bedtimes.
Sleep Duration Calculator
Set your wake-up time to see suggested bedtimes.
This tool is for education and general interest only. It is not a medical device and must not be used to diagnose, treat or make health decisions. Always consult a qualified professional.
How to use it
- Step 1Set the time you must wake up.
- Step 2Adjust how long you take to fall asleep.
- Step 3Pick one of the suggested bedtimes.
Sleep runs in cycles
Sleep is not one long, flat state. It moves through repeating cycles of light sleep, deep sleep and dreaming REM sleep, each lasting roughly 90 minutes.
Waking near the end of a cycle, in lighter sleep, often feels easier than being pulled out of deep sleep by an alarm.
How much sleep do adults need?
Most adults do best with about seven to nine hours a night, which is roughly five to six full cycles. Teenagers and children generally need more.
This tool suggests bedtimes that let you complete whole cycles before your alarm. Learn the science in our sleep guide and the article on why we sleep.
Questions & Answers
Frequently asked questions
On average about 90 minutes, though it varies between people and across the night.
Most adults need seven to nine hours. Children and teenagers need more. Quality matters as much as quantity.
Waking in the middle of deep sleep can cause grogginess. Timing your alarm near the end of a cycle may help.
Understand the science
Go beyond the numbers
Every tool pairs with a guide that explains the biology behind it in plain language.