Wake at 4:00 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 8:15 pm
5 cycles and 7h 30m asleep: the row nearest eight hours.
| Get into bed | Cycles | Time asleep |
|---|---|---|
| 6:45 pm | 6 cycles | 9h |
| 8:15 pm | 5 cycles | 7h 30m |
| 9:45 pm | 4 cycles | 6h |
| 11:15 pm | 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.
What a 4:00 am alarm asks of the evening
Four o'clock puts every row of the table on the evening before. Six cycles means in bed at 6:45 pm, five at 8:15 pm, four at 9:45 pm and three at 11:15 pm. It is the earliest alarm with a written page here, and with 4:30 am one of two where even the three-cycle row is in bed before midnight.
The alarm itself goes off in the dark on every day of the year in London, New York, Johannesburg, Cape Town and Sydney. Even in London in the middle of June, the earliest sunrise of the five cities, the sun is up about forty minutes after it.
The six-cycle bedtime of 6:45 pm is in daylight for about half the year in four of them. In 2026, in London it is light from the day the clocks go forward, 29 March, to late September, and in New York from its own change on 8 March to late September. Cape Town has it light from late September to late March, and Sydney from its clocks going forward on 4 October until they go back on 5 April. Johannesburg, whose sunsets come earlier, has it light only from the end of November to late February.
The five-cycle bedtime of 8:15 pm is in daylight in London from late April to the middle of August, and in New York from late May to late July. In Johannesburg, Cape Town and Sydney it is dark all year, and 9:45 pm is dark in all five cities on every day of the year.
Every bedtime comes before the clocks change, and the alarm comes after, so on the night they go forward every row gives an hour less in bed than the table says, and on the night they go back, an hour more. In 2026 those nights are 29 March and 25 October in London, 8 March and 1 November in New York, and 4 October and 5 April in Sydney. Johannesburg and Cape Town keep the same clock all year, so there the table holds every night.
At the rota planner's starting values, half an hour of travel and an hour to get ready, a 4:00 am alarm is the one for a shift that starts at 5:30 am. The early shift starts at 6:00 am and asks for 4:30 am instead.
Further afield, a 4:00 am alarm rings in daylight only in the far north. In Stockholm it is light from late May to the middle of July, about eight weeks, in Moscow from late May to the second week of July, and in Helsinki and Oslo for about three and a half weeks around midsummer. Copenhagen, Tokyo and even Anchorage never see the sun before 4:00 am, though Anchorage comes within about twenty minutes of it in June.
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 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.