About Sleep Cycle Calculators

Last updated June 5, 2026

I got curious about why some mornings feel awful regardless of how long I slept, read up on 90-minute sleep cycles, and built the bedtime, wake-time, and nap math around them. Everything here is a general estimate, not medical advice.

What’s on this site

Right now there are 6 calculators here: Bedtime Calculator, Wake Time Calculator, Sleep Debt Calculator, Caffeine Cutoff Calculator, Sleep By Age Calculator, and Nap Calculator. Each one is a single-purpose tool that shows its formula, lists its assumptions, and runs on any device with no signup.

Why these are different

A lot of calculators are black boxes — you get a number and no way to tell if it’s right. These work the other way around: the formula, the constants, and a worked example sit on the page next to the result, so you can redo the math by hand. No account, no paywall, no signup.

How the math is kept honest

Each formula is shown in full and was independently re-derived and spot-checked against the calculator’s code. Reference values (typical rates, averages, rules of thumb) are labeled as approximate and are editable, so you can put in your own real numbers. Nothing here is medical advice. The sleep-cycle model is an average; if you have ongoing sleep problems, see a doctor.

Found a mistake?

I’d genuinely like to know. Email [email protected] and I’ll fix it.