Prayer Time Calculation Methods Explained: Why Fajr and Isha Times Differ

Two people in the same city, using two different prayer apps, can see Fajr times twenty minutes apart. Neither app is broken. They are using different calculation methods — different definitions of when dawn begins and when night falls. This guide explains what those methods are, why they differ, and how to pick the right one.

What every method agrees on

Of the five daily prayers, three are defined by events that astronomy pins down precisely:

• Dhuhr begins just after solar noon, when the sun crosses the meridian and starts to decline.
• Asr begins when an object’s shadow reaches a set length (the Asr guide covers the Standard and Hanafi definitions).
• Maghrib begins at sunset, when the upper edge of the sun disappears below the horizon (calculated with a standard allowance of 0.833° for atmospheric refraction and the size of the sun’s disc).

These are the same in every method, apart from small precautionary minutes some timetables add.

The two prayers that differ are the ones defined by twilight:

• Fajr begins at true dawn (al-fajr al-sadiq) — the horizontal whitening of the eastern sky.
• Isha begins when the evening twilight has disappeared (al-shafaq) — the red glow, according to the majority, or the white glow, according to the Hanafi school.

Twilight fades gradually, so “when does dawn begin?” has to be translated into a measurable rule. Methods do this by choosing a sun depression angle: how far below the horizon the sun must be.

The main methods compared

Method	Fajr angle	Isha	Commonly used in
Muslim World League (MWL)	18°	17°	Europe, Far East, parts of the US
Islamic Society of North America (ISNA)	15°	15°	North America
Egyptian General Authority of Survey	19.5°	17.5°	Egypt, parts of Africa, Syria, Lebanon
Umm al-Qura University, Makkah	18.5°	90 min after Maghrib (120 in Ramadan)	Saudi Arabia
University of Islamic Sciences, Karachi	18°	18°	Pakistan, India, Bangladesh, Afghanistan
Gulf Region	19.5°	90 min after Maghrib	Parts of the Gulf
Dubai	18.2°	18.2°	UAE
Kuwait	18°	17.5°	Kuwait
Qatar	18°	90 min after Maghrib	Qatar
JAKIM / Singapore	20°	18°	Malaysia, Singapore, Brunei
KEMENAG	20°	18°	Indonesia
Diyanet	18°	17°	Turkey (with local adjustments)
UOIF	12°	12°	France (some mosques)

A larger Fajr angle means an earlier Fajr; a larger Isha angle means a later Isha. A fixed interval for Isha (Umm al-Qura, Gulf, Qatar) is simple and works well in desert latitudes where twilight is short and predictable.

How much difference does it make?

Here are calculated times for London using each method, on three days of the year:

Method	21 Dec 2026 Fajr / Isha	20 Mar 2027 Fajr / Isha	21 Jun 2026 Fajr / Isha
MWL (18°/17°)	05:59 / 17:51	04:11 / 20:00	02:31 / 23:27
ISNA (15°/15°)	06:20 / 17:38	04:31 / 19:46	02:53 / 23:12
Egypt (19.5°/17.5°)	05:49 / 17:54	04:00 / 20:03	02:20 / 23:30
Umm al-Qura (18.5°/90 min)	05:56 / 17:23	04:07 / 19:43	02:27 / 22:52
Karachi (18°/18°)	05:59 / 17:58	04:11 / 20:07	02:31 / 23:34

Between the earliest and latest methods, Fajr differs by about 30 minutes and Isha by up to 40 minutes. In June, the summer figures also depend on a high-latitude rule, because at London’s latitude the sun never sinks 18° below the horizon in midsummer — a subject covered in our guide to prayer times at high latitudes.

Closer to the equator, the differences shrink. In Karachi or Makkah, twilight is short all year, and methods usually agree within 10–15 minutes.

Where the angles come from

The angles are attempts to capture an observation the Prophet ﷺ described: Fajr begins with the light that “spreads horizontally” across the horizon, not the vertical “false dawn” (al-fajr al-kadhib) that precedes it. Astronomers define astronomical twilight as beginning when the sun is 18° below the horizon — the moment the sky is no longer fully dark — and many Muslim bodies adopted 18° on that basis.

Observation campaigns, however, have produced different results. Some observers in Europe and North America reported seeing true dawn at around 15° or even less, which informed ISNA’s choice. Others, observing in clearer desert skies, supported 18°–19.5°. The JAKIM and KEMENAG 20° angle reflects long-standing practice in Southeast Asia. The variety is not carelessness; it reflects real differences in observation, atmosphere and scholarly judgement.

Which method should you choose?

1. Follow your local mosque. If you pray in congregation, the mosque’s timetable defines when Fajr and Isha are prayed. Ask which method or timetable they use and set your app to match.

2. If you have no local mosque, follow your country’s authority.

• Saudi Arabia: Umm al-Qura
• Pakistan, India, Bangladesh: Karachi, Hanafi Asr
• Egypt: Egyptian General Authority
• Turkey: Diyanet (the official timetable includes local precautionary adjustments)
• Malaysia, Singapore: JAKIM/MUIS
• Indonesia: KEMENAG
• North America: ISNA is common, though many mosques use other methods or local timetables
• UK and Europe: MWL is widespread, but many UK mosques publish their own timetables, sometimes based on local observation

3. Be consistent. Choose one method and use it every day rather than switching to whichever gives the most convenient time.

Precaution (ihtiyat)

Many printed mosque timetables add a few minutes of precaution to some prayers — for example, Maghrib 2–3 minutes after the calculated sunset, or Fajr a few minutes later for the start of prayer while keeping the calculated time for the end of suhoor. These adjustments explain small differences between a mosque timetable and an app using the same method.

For fasting, a common safe practice is to stop eating a few minutes before the calculated Fajr and to break the fast at or just after the calculated Maghrib.

Why some methods use a fixed Isha interval

The Umm al-Qura, Gulf and Qatar methods set Isha at 90 minutes after Maghrib (Umm al-Qura extends it to 120 minutes in Ramadan to accommodate taraweeh). This works well in Arabia for two reasons:

• Twilight is short and stable. At latitudes around 20–26° N, the sun sinks steeply after sunset, so the end of twilight comes about 75–95 minutes after sunset all year round.
• Simplicity for the public. A fixed interval is easy to announce and remember, and it avoids the very late Isha that angle-based methods can give in summer.

Outside the Gulf, especially at higher latitudes, a fixed 90 minutes can be noticeably early in summer and late in winter compared with the actual twilight, which is why other regions use angles.

Three quick checks for any prayer app

1. Location: make sure the app uses your real city, not a capital hours away. A few hundred kilometres east or west shifts every prayer by several minutes.
2. Method and Asr school: set them deliberately. Many apps default to MWL and Standard Asr, which may not match your mosque.
3. High-latitude rule: if you live above about 48° N, check the rule used for summer Fajr and Isha.

Then compare the app with your mosque’s timetable for a week. If Dhuhr and Maghrib agree but Fajr and Isha do not, the method is the difference.

How our prayer times work

Our prayer times page calculates times in your browser from your city’s coordinates and time zone. It defaults to the method most commonly used in your country — for example Karachi with Hanafi Asr in Pakistan, Umm al-Qura in Saudi Arabia, and ISNA in North America — and lets you change the method, the Asr school and the 12/24-hour format. We have checked our calculations against the Aladhan prayer-time service: across several cities and methods, the results agree within a minute.

Summary

• Dhuhr and Maghrib are the same in every method; Fajr and Isha depend on the twilight angle chosen.
• Common angles: 15° (ISNA), 18° (MWL, Karachi), 18.5° (Umm al-Qura), 19.5° (Egypt), 20° (Southeast Asia).
• Differences are largest at high latitudes and in summer — up to 30–40 minutes in London.
• Follow your local mosque or national authority, and stay consistent.