This sleep calculator suggests the best times to fall asleep or wake up so that you rise at the end of a sleep cycle rather than in the middle of one. Waking between cycles tends to feel easier and less groggy.
For example, to wake up at 7:00 AM feeling rested, a good bedtime is around 9:45 PM or 11:15 PM.
How Sleep Cycles Work
Sleep moves through cycles that last about ninety minutes each, passing through light sleep, deep sleep, and dream sleep. A full night is usually five or six cycles. This calculator counts back or forward in ninety minute steps and adds the time it takes you to fall asleep, which is fifteen minutes by default.
Two Ways to Use It
Wake up at a set time
Enter the time you need to wake up and the calculator shows the bedtimes that line up with complete cycles.
Go to sleep now
Switch the mode and enter your bedtime, and it shows the best times to set your alarm.
How Much Sleep Do You Need
Most adults do well with seven to nine hours, which is about five to six full cycles. Teenagers and children generally need more. Use the suggestions as a helpful guide rather than a strict rule, since everyone is a little different.