Bedtime Calculator
Calculator methodology
How the calculator turns one clock time into planning suggestions—and what those suggestions cannot tell you.
The formula
The calculator adds or subtracts two to six 90-minute planning blocks, then accounts for the selected fall-asleep buffer. Displayed times round up to the next five minutes.
Why 90 minutes is only an estimate
Sleep stages repeat, but cycle length varies between people and across the night. The model cannot measure a person’s stages or predict the exact moment they will wake.
How to use the result
Prefer options that allow enough total sleep. Treat cycle timing as a rough scheduling aid, not a guarantee. Adults generally need at least seven hours, although needs vary.
Sources and limits
Our baseline sources include the NINDS overview of sleep stages and CDC sleep guidance. The calculator does not diagnose insomnia, sleep apnea, or any other condition.
Questions or corrections? Contact us.