About Sleep Math Calculators

Last updated June 9, 2026

Sleep math is model math. The 90-minute sleep cycle is an average, the time it takes to fall asleep is an average, and caffeine’s roughly five-hour half-life is an average too. Every calculator on this site says which model it’s using — and where that model stops fitting real people.

The calculators

The site currently has 6: Bedtime Calculator, Wake Time Calculator, Sleep Debt Calculator, Caffeine Cutoff Calculator, Sleep By Age Calculator, and Nap Calculator.

Averages, clearly labeled

Bedtimes are computed by counting back in 90-minute cycles plus a buffer for falling asleep, and both numbers are shown and adjustable — real cycles run anywhere from about 80 to 110 minutes. The caffeine page applies exponential decay with its half-life assumption in the open.

Where the model ends

Nothing here is medical advice. The sleep-cycle model is an average; if you have ongoing sleep problems, see a doctor.

Improve the math

If the sleep science here lags the literature, email corrections@sleepmathcalc.com — the model gets re-checked against current sources.