Accurate prayer times rest on three things: your exact location, the right calculation method for your region, and any manual adjustments. But to configure them well, it helps to understand where these times come from, and why two apps can show two different times for the same Fajr. A short detour through astronomy, then the practical setup.
“Indeed, prayer has been decreed upon the believers a decree of specified times.” — Quran 4:103
The astronomy behind the times
Each prayer is indexed to a precise solar event, observable with the naked eye. That's how Muslims determined the times for fourteen centuries, long before apps:
- Fajr: true dawn, when the first diffuse light appears on the eastern horizon. The sun is still 12 to 18° below the horizon.
- Shuruq: sunrise, the end of Fajr time.
- Dhuhr: just after the sun crosses the meridian (the zawal), its highest point in the sky.
- Asr: when an object's shadow reaches a given length (more on this below).
- Maghrib: the complete setting of the solar disk.
- Isha: the disappearance of the red then white twilight glow, when the sun is again 12 to 18° below the horizon, to the west.
A detail that often surprises: Dhuhr almost never falls at 12:00. Clock time is offset from solar time: time zones, daylight saving, and an astronomical oscillation called the equation of time (up to ±16 minutes depending on the season). In Paris in summer, the zawal happens around 1:50 pm. A prayer app simply redoes, to the second, the calculation that sky observation used to provide.
1. Location first
The whole calculation depends on your latitude and longitude. The order of magnitude to remember: 1° of longitude ≈ 4 minutes of shift on every time. Two options:
- GPS: the app uses your location “while in use”, never permanently in the background.
- Manual city: enter your city if you'd rather not enable location. City-level precision is more than enough: across a metropolitan area, the difference is measured in seconds.
2. Choose the right calculation method
Sunrise and sunset are objective instants, but Fajr and Isha depend on a matter of judgement: at what solar angle below the horizon does dawn become visible? The answer varies with atmosphere, latitude and light pollution, which is why institutions adopted different conventions:
- Mosquée de Paris (12° / 12°), recommended in France: at French latitudes, an 18° angle yields very early Fajr in summer, and 12° matches local observation better.
- Muslim World League (18° / 17°), the most widespread convention worldwide, faithful to the astronomical definition of twilight.
- Umm al-Qura (Saudi Arabia): 18.5° for Fajr, and Isha fixed at 90 minutes after Maghrib.
- ISNA (15° / 15°), Karachi (18° / 18°), Egypt (19.5° / 17.5°)…, depending on your region and local convention.
There is no single “true” method and “false” ones: they are different readings of the same phenomenon. The right reflex: ask your local mosque which method it uses, then select the same one in the settings. You'll be aligned with your community.
3. The high-latitude problem
Above roughly 48° of latitude (northern France, Belgium, the UK), something happens at the height of summer: the sun never dips 18° below the horizon. Astronomical twilight never ends: mathematically, Isha “no longer exists”. Scholars proposed several solutions: take one-seventh of the night, use the proportion of the last “normal” night, or follow a reference city. Good apps apply one of these rules automatically; it's also one reason the 12° convention was chosen in France, since it remains computable almost all summer.
4. The Asr school
Asr is defined by shadow length, and two conventions coexist:
- Majority (Shafi'i, Maliki, Hanbali): when an object's shadow equals its height (plus the residual shadow at zawal).
- Hanafi school: when the shadow reaches twice the height, an Asr roughly one hour later.
Simply pick the school you follow in the settings; both are legitimate.
5. Fine-tune with adjustments
Even with the same method, your mosque's official timetable may differ by a few minutes: rounding, precaution margins, the altitude of the place. A per-prayer adjustment setting (± a few minutes) lets you align the app exactly with the timetable your community follows.
Why two apps show different times
Almost always one of these four reasons: a different default method (by far cause #1), a slightly different position, different high-latitude rules, or different rounding (up or down to the minute). It's not a bug, it's a convention to harmonise.
In summary: the checklist
- Exact location (GPS or your city);
- Calculation method = your mosque's (in France: Mosquée de Paris 12°/12° by default);
- Asr school according to your school of jurisprudence;
- Fine adjustments if needed, prayer by prayer.
And with Deenius, all this astronomical calculation runs on your iPhone, offline, with no data, not even your location, ever leaving the device.