Sleep Time Calculator

Say you have to be up at 6:30 for a train. Put that into the Bedtime tab and Sleep Time Calculator counts back in 90-minute blocks, then adds about 14 minutes for falling asleep. You get a short list of times to be in bed with the lights off, not times to start getting ready. The Wake-up tab runs the same math forward from whenever you're going to bed. A Nap tab covers 10, 20, 30, 60 and 90 minutes, and the page explains that the awkward middle lengths, around 30 minutes, are the ones most likely to leave you groggy.

Five cycles, about 7.5 hours of sleep, is the default the page suggests for most adults. Six cycles is the pick after a hard week or an illness. Three or four cycles get labeled as a stopgap for one bad night, below adult guidance, rather than a schedule to repeat.

The most useful thing here is how carefully the site labels its assumptions. The 90-minute cycle is described as an adult average that often runs anywhere from 70 to 120 minutes in real recordings. The 14-minute buffer is a middle value from studies that put typical sleep onset at 10 to 20 minutes. The site even says the familiar idea that 7.5 hours feels better than 8 is a planning shortcut rather than a lab finding.

If you already know your cycles run long or short, a separate sleep cycle calculator lets you set the cycle length and fall-asleep time yourself. Figures on the main page carry numbered citations to sources such as the AASM adult sleep consensus statement and a StatPearls chapter on sleep stages.

This is a timing aid, and the page says so. It doesn't diagnose anything, and it tells people who regularly take more than 30 minutes to fall asleep, snore loudly or wake unrefreshed to talk to a clinician. The About page adds that no named clinical reviewer has checked the medical claims yet.

The calculators run in your browser without an account, and the privacy policy (updated August 25, 2026) says the times you enter aren't sent to the site's servers. The site does use Google Analytics and shows Google AdSense ads, which can set third-party advertising cookies.