How Prayer Times Are Calculated, and Why Apps Disagree

Prayer times are calculated from the position of the sun at your location. Dhuhr, Asr and Maghrib follow clear astronomical markers, but Fajr and Isha depend on how far below the horizon the sun is taken to be, an angle that differs between methods such as the Muslim World League (18° and 17°) or ISNA (15° and 15°). The method, the Asr school and the rule used for high latitudes explain why two apps, or an app and your mosque, can differ by several minutes.

The five prayers and the sun

• Fajr begins at true dawn, when the sun is a certain angle below the eastern horizon, and ends at sunrise.
• Dhuhr begins just after solar noon, when the sun passes its highest point.
• Asr begins when the shadow of an object reaches a certain length (see below).
• Maghrib begins at sunset.
• Isha begins when twilight has faded, when the sun reaches a certain angle below the western horizon. Some methods use a fixed interval after Maghrib instead.

Sunrise, noon and sunset are easy to agree on. The debate concerns twilight: at what point does dawn begin, and when does dusk end?

Fajr and Isha angles: the main methods

Method	Fajr	Isha
Muslim World League (MWL)	18°	17°
Islamic Society of North America (ISNA)	15°	15°
Egyptian General Authority of Survey	19.5°	17.5°
Umm al-Qura (Makkah)	18.5°	90 minutes after Maghrib
UOIF (France)	12°	12°

The larger the angle, the earlier Fajr and the later Isha. The difference between 18° and 15° can mean twenty minutes or more, and much more in a British summer. Other methods exist too, for example the Moonsighting Committee method, which uses 18° with seasonal adjustments and is offered by some apps for the UK and North America.

Asr: two schools

For Asr, the question is the length of an object's shadow:

• Standard (Shafi'i, Maliki, Hanbali): Asr begins when the shadow equals the object's length, plus the shadow it had at noon.
• Hanafi: Asr begins when the shadow equals twice the object's length, plus the noon shadow.

The Hanafi Asr is therefore later, often by half an hour to an hour or more depending on the season and latitude. Depending on the community, a UK mosque may follow either, and some timetables show both.

High latitudes: the British summer problem

In London, around the summer solstice, the sun dips only about 15° below the horizon at its lowest point; in Edinburgh, only about 11°. An 18° angle is therefore never reached for several weeks: astronomically, Fajr and Isha by that definition do not occur. Every timetable must use a rule for these weeks. The most common are:

• Middle of the night: Isha no later, and Fajr no earlier, than the midpoint between sunset and sunrise.
• One-seventh of the night: the night is divided into seven parts; Isha comes after the first seventh, Fajr at the start of the last seventh.
• Angle-based: the portion of the night is set in proportion to the chosen angle.

Some mosques also adopt a smaller angle in summer or follow a timetable agreed by local scholars. These are religious decisions: ask your mosque which rule it uses.

Why two apps show different prayer times

1. Calculation method: MWL, ISNA, Umm al-Qura… each gives a different Fajr and Isha.
2. Asr school: standard or Hanafi.
3. High-latitude rule: decisive between May and August in the UK.
4. Location: a city centre or your exact address; from one end of a large city to the other, times can move by a minute or two.
5. Safety margins: some timetables add a few minutes of precaution (ihtiyat) to certain prayers.
6. Start time or congregation time: a mosque timetable often lists both. Comparing an app's start time with a jama'ah time creates false differences.

Ramadan timetables and imsak

During Ramadan, many mosques publish a dedicated timetable showing the end of suhoor and the time of iftar. Some add an "imsak" time, a few minutes before Fajr, as a precaution for stopping eating. The time that matters for the fast is still Fajr, and the margin chosen is a decision of each mosque. If your device shows Fajr and your mosque's calendar shows imsak, the few minutes between them are not an error.

How to align your prayer times with your mosque

1. Get your mosque's timetable for the current month, start times rather than jama'ah times.
2. Set your city or exact location.
3. Choose the Asr school your mosque follows.
4. Try the methods one by one and keep the closest, especially for Fajr and Isha.
5. Fine-tune: adjust the angles or add a few minutes to individual prayers.
6. Check again each month and at the clock changes, because the gap between a method and a mosque timetable can drift with the seasons.

Our guide on getting your mosque's prayer times at home compares the ways to follow a mosque timetable day to day.

How Nida Home calculates prayer times

Nida Home calculates prayer times directly on the device, without relying on an external server, so the times and the adhan stay available without internet. You can choose:

• a method: Muslim World League, ISNA, Egypt, Umm al-Qura or UOIF;
• custom Fajr and Isha angles;
• the Asr school, Shafi'i or Hanafi;
• a high-latitude rule, useful for British summers;
• an adjustment for each prayer from −60 to +60 minutes, to match your mosque's timetable.

The Hijri date is also calculated and displayed on the device. Sources are documented on our Authenticity & sources page.

Frequently asked questions

Which prayer time calculation method should I use in the UK?

The one your local mosque follows. Ask which method, Asr school and summer rule it uses, then adjust your device to match its timetable.

Why is my app's Fajr different from my mosque's?

Usually because of a different angle, a different high-latitude rule in summer, or because you are comparing with the jama'ah time rather than the start time.

What is the difference between Hanafi and Shafi'i Asr?

The Hanafi Asr begins when an object's shadow is twice its length (plus the noon shadow), the Shafi'i when it equals its length. The Hanafi time is therefore later.

Why are Isha and Fajr so close together in summer?

At UK latitudes the sun stays close to the horizon at night around June, so twilight barely ends. Timetables use special rules for these weeks.