I built this after getting annoyed at my own alarm clock. Every sleep cycle calculator I tried had the same two problems. It counted from the moment I got into bed, not from the moment I actually fell asleep — so on a bad night the math was off by 20 minutes and I'd still wake up mid-cycle. And it dumped six times on screen with no sign of which were worth taking seriously. So I added a 14-minute average sleep-onset buffer, plus a quality label on every result. Then I got carried away and built three more tools I wanted for myself: a nap calculator that separates light-sleep naps from full cycles, jet lag recovery, and sleep debt. The part I'm most deliberate about is what the site refuses to do. Every cycle number is cited to NSF / AASM / CDC guidance, and a section called "What This Calculator Is Not" says plainly that it won't diagnose insomnia or apnea. Timing aids shouldn't pretend to be diagnoses. Free, no sign-up, no install. Curious which tool you'd actually use day to day.

Sleep Time Calculator

Find your ideal bedtime and wake-up time in seconds

Find your ideal bedtime and wake-up time in seconds