Why prayer time apps disagree — and how to fix yours

If you have ever had two prayer time apps open side by side and seen a twenty-minute difference in Fajr, you have run into one of the most misunderstood parts of Islamic scheduling software. Neither app is necessarily broken. They are answering slightly different questions.

Here is how the calculation actually works, in plain language.

Solar geometry, not a lookup table

Prayer times are not stored in a database somewhere. They are computed from the position of the sun relative to your exact location on a given date. Given latitude, longitude, date and time zone, the sun's altitude at any moment can be calculated precisely. Each prayer is defined by a specific solar condition:

• Fajr — when the sun reaches a set angle below the horizon before sunrise (dawn).
• Dhuhr — just after the sun crosses the meridian (its highest point).
• Asr — when an object's shadow reaches a defined multiple of its own length, plus the shadow length at noon.
• Maghrib — at sunset.
• Isha — when the sun reaches a set angle below the horizon after sunset (nightfall).

Sunrise, sunset and solar noon are astronomically fixed. That is why Dhuhr and Maghrib rarely differ much between apps. The disagreements live in Fajr, Isha and Asr.

Difference 1: the twilight angle

Dawn and nightfall are not instants; they are transitions. Different authorities settled on different sun angles to mark them:

• Muslim World League: 18° for Fajr, 17° for Isha
• Islamic Society of North America (ISNA): 15° and 15°
• Egyptian General Authority of Survey: around 19.5° and 17.5°
• Umm al-Qura (Makkah): 18.5° for Fajr, and Isha at a fixed interval after Maghrib rather than an angle
• University of Islamic Sciences, Karachi: 18° and 18°

A three-degree difference in the Fajr angle can move the time by fifteen to twenty-five minutes depending on your latitude and the season. That is your twenty-minute gap, and it is a legitimate difference of convention rather than a bug.

Difference 2: the Asr school

The Shafi'i, Maliki and Hanbali position takes Asr when an object's shadow equals its own length plus the noon shadow. The Hanafi position uses twice the object's length. In practice that is often around an hour apart. If your app's Asr is consistently late compared with your mosque, this setting is almost always the reason.

Difference 3: high latitude rules

Above roughly 48° latitude, there are parts of the year when the sun never dips far enough below the horizon for true dawn or nightfall to occur. The geometry produces no answer at all. Communities resolved this with conventions:

• Middle of the night — split the night between Maghrib and sunrise; Isha and Fajr sit around that midpoint.
• One-seventh of the night — divide the night into seven parts for the Isha and Fajr portions.
• Angle-based — derive an interval from the twilight angle you already use.
• Nearest latitude — borrow times from a fixed lower latitude.

In Northern Europe and Canada, two apps using different high-latitude rules can differ by more than an hour in June. Both are following a recognised convention.

Difference 4: local adjustments

Many mosques announce their adhan a few minutes after the calculated time, for practical reasons. An app configured to match one mosque exactly will differ from a purely astronomical calculation. This is why per-prayer minute adjustments exist in most serious apps.

Which method should you use?

The generally recommended approach is simple: use the method your local mosque uses. Prayer is communal, and matching the community around you matters more than choosing the convention with the most elegant argument behind it. If you do not know, ask at the mosque — many publish their method and angle on their timetable.

What to check when the times look wrong

1. 1.Is the calculation method the same as your mosque's?
2. 2.Is the Asr school set to the one you follow?
3. 3.Is your location accurate, and is your time zone set automatically?
4. 4.If you live at high latitude, which rule is applied for Fajr and Isha?
5. 5.Are per-prayer adjustments needed to match your mosque exactly?

Those five checks resolve nearly every "the app is wrong" report we receive for Salah Companion.

The takeaway

A prayer time app is a calculator, and a calculator's answer is only as meaningful as the convention it was given. Understanding which convention you are using turns an app from something you either trust or distrust into something you can actually verify.