Wake at 4:00 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 8:15 am
5 cycles and 7h 30m asleep: the row nearest eight hours.
| Get into bed | Cycles | Time asleep |
|---|---|---|
| 6:45 am | 6 cycles | 9h |
| 8:15 am | 5 cycles | 7h 30m |
| 9:45 am | 4 cycles | 6h |
| 11:15 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.
A 4:00 pm alarm before a night shift
An alarm at four in the afternoon is the shape sleep takes before a night shift. The bedtimes are 6:45 am, 8:15 am, 9:45 am and 11:15 am, and every one of them comes after the hour at which any of these five cities changes its clocks, so the table holds on those nights too.
The five-cycle row, 8:15 am, is a twelve-hour night ending at 7:00 am, plus an hour and a quarter to get home. From a 4:00 pm alarm to a 7:00 pm start is three hours; to the 10:00 pm start of the eight-hour night rota it is six.
The 8:15 am, 9:45 am and 11:15 am bedtimes are in daylight everywhere, all year. The six-cycle row at 6:45 am is light in London from early March to late September, in New York from late February to late September except for the three weeks after the clocks go forward in March, and again in the first half of November, in Johannesburg for all but about ten weeks in winter, in Cape Town from the middle of September to the middle of March, and in Sydney from early August to early March and again for about seven weeks from early April.
The alarm is in daylight on every day of the year in New York, Johannesburg, Cape Town and Sydney. In London it rings after sunset from late November to the end of December, when the sun goes down as early as 3:51 pm.
Further afield, the 6:45 am bedtime is in daylight in Nairobi on every day of the year and in Tokyo on all but about six weeks around the new year. Singapore misses it on every day by a single minute, since sunrise there never comes before 6:46 am. Madrid has it for only about three weeks in June. Berlin and Moscow share London's December problem with the alarm: in Berlin it rings after sunset from late November to the end of December, and in Moscow for about three weeks from early December.
At the planner's default of an hour to settle, a twelve-hour night that ends at 7:00 am puts bed at 8:00 am, and five cycles from there end at 3:45 pm, a quarter of an hour before this page. The six-cycle row starts at 6:45 am, before a twelve-hour night has ended, so it only fits a shift that finishes by 5:45 am. For the eight-hour night rota, which ends at 6:00 am, the same row leaves three quarters of an hour between finishing and bed. On the night the clocks go forward, the shift that follows this alarm is an hour shorter than its rota says, and on the night they go back an hour longer, in every city here that changes its clocks. Johannesburg, Cape Town, Tokyo, Singapore, Nairobi and Dubai do not. In Tokyo the sun sets as early as 4:28 pm in late November and early December, half an hour after this alarm, and New York's earliest sunset, 4:28 pm in early December, gives the same half hour. Singapore, Nairobi and Dubai keep the afternoon much longer: none of them sees the sun set before 5:28 pm.
Sunrise and sunset: the NOAA solar equations, for each city centre in 2026, to the nearest minute.
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 4:00 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.