Wake at 9:15 am
Four bedtimes, each one a whole number of sleep cycles before the alarm, with a quarter of an hour allowed for actually falling asleep.
Go to bed at 1:30 am
5 cycles and 7h 30m asleep: the row nearest eight hours.
| Get into bed | Cycles | Time asleep |
|---|---|---|
| 12:00 am | 6 cycles | 9h |
| 1:30 am | 5 cycles | 7h 30m |
| 3:00 am | 4 cycles | 6h |
| 4:30 am | 3 cycles | 4h 30m |
7h 30m asleep
The night nearest eight hours, laid on a clock face.
The two assumptions
Move either one and every time above moves with it. The settings follow you around the site.
Reading the table
Six cycles wants 12:00 am and three wants 4:30 am, and between those two ends sits 4 and a half hours of sleep — and the same 4 and a half hours of evening, which is the trade the table is really offering.
Every line here falls after midnight, so the date on the calendar has already turned.
Every time on this page comes from two numbers: a cycle of 90 minutes and 15 minutes between getting into bed and being asleep. Neither is a measurement of you. The reference pages say where each one comes from.
A quarter of an hour either way
If the alarm is set to something near but not exactly 9:15 am, the table for it is a page of its own.
The other direction
Already in bed and deciding when to set the alarm? The sleep-now page runs the same sum forwards from the time where you are.