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Sleep Schedule Calculator
Find the best times to wake up or go to sleep based on 90-minute sleep cycles. Shows all optimal times. Free.
The Sleep Calculator is a free online tool that helps you find the best times to wake up or go to sleep based on 90-minute sleep cycles. shows all optimal times. free It runs in your browser with no sign-up, downloads, or installation needed. All processing happens locally — your data stays on your device.
Sleep Calculator
💡 Each sleep cycle lasts about 90 minutes. Waking at the end of a cycle means you wake in light sleep — feeling more refreshed. Add 15 minutes for the average time it takes to fall asleep.
How to use
1
Sleep cycles
A full sleep cycle is approximately 90 minutes, cycling through light sleep, deep sleep (NREM) and REM (dream) sleep. Most people complete 4–6 cycles per night. Waking during deep sleep leaves you feeling groggy — waking at the end of a cycle feels more natural and refreshing.
2
How many cycles?
5–6 cycles (7.5–9 hours) is ideal for most adults. 4 cycles (6 hours) is a minimum for most people. Less than 4 cycles impairs cognitive function. The NHS recommends 7–9 hours for adults. Teenagers need 8–10 hours, children even more.