Wake at 3:15 pm
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 7:30 am
5 cycles and 7h 30m asleep: the row nearest eight hours.
| Get into bed | Cycles | Time asleep |
|---|---|---|
| 6:00 am | 6 cycles | 9h |
| 7:30 am | 5 cycles | 7h 30m |
| 9:00 am | 4 cycles | 6h |
| 10:30 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 6:00 am and three wants 10:30 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 is a bedtime on the same evening. None of them crosses midnight.
A wake time this late in the day reads as a night-shift schedule: the sleep runs through the morning rather than through the night, and the arithmetic does not care which.
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 3:15 pm, 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.