Plan bedtime or wake-up times to align with complete 90-minute sleep cycles — including a 15-minute fall-asleep buffer — for better morning alertness.
Overview
A sleep cycle lasts about 90 minutes and moves through light sleep, deep sleep, and REM. Waking between cycles — not in the middle of one — helps you feel more refreshed.
This calculator subtracts or adds complete cycles plus a 15-minute fall-asleep buffer so you can pick a practical bedtime or wake-up window.
Most adults do well with 4–6 cycles (about 6–9 hours of sleep). Use Sleep now when you are going to bed immediately. Timing helps, but sleep hygiene still matters.
Steps
Pick wake-up time planning or bedtime planning.
Set the time you need to wake up, or the time you plan to go to bed (24-hour format).
Uses the current time as bedtime and shows wake-up options right away.
Compare 3–6 cycles with quality labels (Optimal through Minimum).
Prefer the Recommended (5-cycle) option when your day allows it.
Math
Bedtime = Wake Time − (Cycles × 90 min) − 15 min · Wake = Bedtime + 15 min + (Cycles × 90 min)
Cycle-based timing estimates sleep windows that reduce waking mid-cycle. The 15-minute buffer accounts for typical sleep onset.
Worked cases
06:00 − 7h30m − 15m
Bedtime about 22:15
07:00 − 6h − 15m
Bedtime about 00:45
23:15 + 4–6 × 90 min
Wake options about 05:15, 06:45, or 08:15
Why use this
Questions