EV-G11Everyday reference

Sleep cycles and bedtime math

A bedtime calculator is subtraction dressed up as biology. The subtraction is exact; the biology is an average.

Count backward from the alarm

Bedtime equals wake time minus whole sleep cycles minus the time you take to fall asleep. Six cycles of 90 minutes is nine hours of sleep.

WAKE TIME− CYCLES × 90 min− FALL-ASLEEP TIME= BEDTIME

Ninety minutes is an average, not a law

Real cycles run shorter and longer, change through the night, and differ between people. The calculator compares planning options; it does not measure your sleep.

Cycles	Sleep	Wake at 7:00 AM → bed by
6	9 h	9:45 PM
5	7.5 h	11:15 PM
4	6 h	12:45 AM

Duration still matters more than timing

The CDC advises seven or more hours for most adults. Consistent schedules, light exposure, and caffeine timing move sleep quality more than hitting an exact cycle boundary.

Boundary: persistent trouble sleeping, loud snoring, or daytime sleepiness are conversations for a clinician, not a calculator.

1 SOURCESource ledger

Check the basis.

01Centers for Disease Control and Prevention — About sleep ↗

QUESTIONS THIS ANSWERS

Questions this answers

How long is a sleep cycle?
What time should I go to bed to wake at 6?