Use this free online sleep calculator to find the best bedtime or wake-up time based on 90-minute sleep cycles, so you wake up feeling rested instead of groggy.
How to Use the Sleep Calculator
Choose "I want to wake up at..." if you have a fixed wake-up time, or "I want to sleep at..." if you're going to bed now.
Enter the time.
Click "Calculate" to see several bedtime or wake-up options, each aligned to a whole number of sleep cycles.
Frequently Asked Questions
A full sleep cycle (light sleep, deep sleep, and REM sleep) takes about 90 minutes on average. Waking up at the end of a complete cycle, rather than in the middle of one, generally feels less groggy.
It accounts for the average time it takes a person to actually fall asleep after getting into bed, so the sleep-cycle math lines up with your real bedtime rather than the moment you lie down.
Yes, it's completely free and requires no sign-up.