Almost every app, wall chart and mosque timetable prints prayer times as five single moments: Fajr 04:51, Dhuhr 13:04, and so on. That presentation is convenient and it is also the source of a persistent misunderstanding, because a prayer time is not a moment. It is the opening of a window, and the prayer is valid at any point until that window closes.
Knowing where the windows close is what turns a missed prayer into a late one. The difference matters: a prayer offered inside its window, however late, is simply the prayer, while one offered after the window has shut is a make-up. So it is worth knowing how much room you actually have — and the honest answer is that it varies enormously by prayer, by season and by latitude.
Where each window ends
The boundaries are defined by the sun rather than by the clock, and four of the five are marked by the start of the next event.
- Fajr ends at sunrise. Not at Dhuhr. This is the one people most often get wrong, because the printed timetable shows Fajr and then Dhuhr and the eye fills in the gap. The window runs from true dawn to the first edge of the sun, and it is the shortest window of the day in summer at almost every latitude.
- Dhuhr ends when Asr begins. Dhuhr opens once the sun has passed its highest point and runs until the Asr shadow length is reached. Because Asr's definition differs between schools, so does the end of Dhuhr — see below.
- Asr ends at sunset. The window runs to Maghrib. There is a widely reported dislike of delaying Asr until the sun has yellowed near the horizon, so the practical window is shorter than the arithmetic one, but the prayer remains valid until the sun is gone.
- Maghrib ends when Isha begins. The shortest window of the day in most places, and in the tropics it is brutally short — the twilight that defines it lasts barely over an hour.
- Isha ends at midnight, or at dawn. Here the schools genuinely differ. The commonly taught preferred limit is the midpoint between sunset and dawn — solar midnight, not 00:00 on the clock — while the outer limit, beyond which it is a make-up, is the arrival of Fajr. Praying Isha at 01:00 is late; it is not usually a missed prayer.
How wide the windows actually are
We computed the windows with the adhan library, Muslim World League angles, Shafi'i Asr, for 21 June and 21 December 2026. The figures are hours from the opening of each prayer to its close.
| City | Fajr | Dhuhr | Asr | Maghrib |
|---|---|---|---|---|
| London | 3.7h | 4.4h | 4.0h | 3.7h |
| Istanbul | 2.1h | 4.0h | 3.5h | 2.0h |
| Cairo | 1.6h | 3.6h | 3.5h | 1.5h |
| Mecca | 1.4h | 3.3h | 3.4h | 1.3h |
| Singapore | 1.3h | 3.4h | 2.7h | 1.2h |
| City | Fajr | Dhuhr | Asr | Maghrib |
|---|---|---|---|---|
| London | 2.1h | 1.6h | 2.3h | 2.0h |
| Istanbul | 1.6h | 2.3h | 2.3h | 1.6h |
| Cairo | 1.4h | 2.8h | 2.3h | 1.4h |
| Mecca | 1.3h | 3.0h | 2.4h | 1.2h |
| Singapore | 1.3h | 3.4h | 2.6h | 1.2h |
What the tables show
Two things stand out. The first is that no window in this table exceeds four and a half hours, and most sit between one and three — the mental model of "I have until the next prayer, which is ages away" is simply wrong. The second is that London in December has a Dhuhr window of one hour and thirty-six minutes. In a British winter, the entire span in which Dhuhr can be prayed fits inside a long lunch break, which is exactly the scenario that makes praying at work a scheduling problem rather than a spiritual one.
Singapore illustrates the opposite constraint. Near the equator the twilight is nearly vertical and it passes fast: the Maghrib window is 1.2 hours in June and 1.2 hours in December, year-round, with no seasonal relief at all.
The Asr boundary is a choice, and it moves two windows at once
Asr is defined by shadow length: it begins when an object's shadow equals its own length plus the shadow it cast at noon (the Shafi'i, Maliki and Hanbali position), or twice its length plus the noon shadow (the Hanafi position). Because Asr's start is also Dhuhr's end, choosing a school moves both boundaries together.
We measured the size of that shift on 21 June 2026. The knock-on effect on the Asr window is severe, because its end — sunset — does not move: the later start is subtracted from the window in full.
This is not a minor setting. If your app is configured to a school your mosque does not follow, you can be praying Asr inside a window your community considers to still be Dhuhr — for well over an hour. It is worth checking which reckoning your app uses, and the related question of which angles it uses for Fajr and Isha, which we measured separately in why prayer time apps disagree.
| City | Shafi'i window | Hanafi window | Asr starts later by |
|---|---|---|---|
| London | 4.0h | 2.7h | 75 min |
| Istanbul | 3.5h | 2.3h | 74 min |
| Cairo | 3.5h | 2.1h | 78 min |
| Mecca | 3.4h | 2.1h | 79 min |
| Singapore | 2.7h | 1.7h | 57 min |
What this means in practice
The useful conclusion is not to pray at the edges. The windows are the outer limits of validity, not a schedule to aim at, and the reported merit of praying at the beginning of the time is the reason most people are taught to treat the printed time as the target.
But knowing the boundaries changes how you handle the ordinary failures of a working day. Waking at 06:20 with Fajr printed at 04:51 is not automatically a missed prayer — the question is whether the sun is up, and in London in December sunrise is after 08:00, so it is not. Realising at 22:40 that Isha was at 20:32 is not a crisis either. Both of those are prayers to offer now, not make-ups to count.
If you do end up outside a window, the procedure is straightforward and it is covered in making up missed prayers.
Common questions
- How late can I pray Fajr?
- Until sunrise, not until Dhuhr. The window runs from true dawn to the moment the sun's edge appears. In London on 21 June 2026 that is 3.7 hours; in Singapore it is 1.3 hours year-round.
- Can I pray Asr just before sunset?
- It is valid until the sun sets, though delaying it until the sun has yellowed near the horizon is widely discouraged. The arithmetic window ends at Maghrib; the recommended window ends earlier.
- Does Isha's time end at midnight?
- At solar midnight — the midpoint between sunset and dawn — rather than 00:00 on the clock, and that is the preferred limit rather than the outer one. The outer limit, past which it becomes a make-up, is the arrival of Fajr.
- Why does my app show Asr an hour later than my mosque?
- Almost certainly a Hanafi versus Shafi'i shadow-length setting. We measured the gap at 74 to 79 minutes across London, Istanbul, Cairo and Mecca on 21 June 2026. Changing the madhab setting in your app will align it.