Sleep calculator
Sleep runs in roughly 90-minute cycles, and waking between cycles feels better than waking mid-cycle. Pick your wake time and see when to fall asleep.
Times include ~15 minutes to fall asleep. Cycles are 90-minute averages.
Frequently asked questions
Why 90-minute cycles?
A full sleep cycle (light, deep, then REM) averages about 90 minutes, and waking at the end of one leaves you in the lightest stage. It is an average, not a law: real cycles run 80 to 110 minutes and lengthen through the night, so treat these times as good targets rather than precision.
Why does the calculator add 15 minutes?
Falling asleep takes most people around 10 to 20 minutes; the suggested bedtimes include a 15-minute buffer so the cycles start when you are actually asleep, not when you lie down.
How many cycles should I aim for?
Five cycles (7.5 hours of sleep) suits most adults, and six (9 hours) fits teenagers and heavy training days. Four (6 hours) works as an occasional floor, not a habit.
Is this medical advice?
No. It is arithmetic on averages. Persistent trouble sleeping or daytime exhaustion despite adequate hours is worth raising with a doctor.