Sleep Calculator

Suggested bedtimes or wake times using 90-minute sleep cycles.

Sleep Calculator helps you suggested bedtimes or wake times using 90-minute sleep cycles. Enter hour (0–23) and minute, review the breakdown, and use the guidance below to understand what the number means — and what it does not. What the Sleep calculator does Sleep Calculator is built for body measurements, calories, and everyday health math. Suggested bedtimes or wake times using 90-minute sleep cycles. You enter hour (0–23) and minute, then Simple Calculators computes the result instantly. These tools use widely published formulas. They are educational screens, not a diagnosis. How the math works Under I want to, choose whether you have a set wake time or a set bedtime, then enter the Hour (0–23, on the 24-hour clock) and Minute. The calculator allows 15 minutes to fall asleep and counts back (or forward) in 90-minute sleep cycles. It suggests times for 6, 5 and 4 cycles — 9, 7½ and 6 hours of sleep. The formula: Bedtime = wake time − 15 min − cycles × 90 min. Waking at the end of a 90-minute cycle tends to feel easier. Most adults need 5–6 cycles.