How Prayer Times Are Calculated: The Science Behind Islamic Salah Timings

The five daily prayers in Islam are tied to the sun's position, not fixed clock times. This is why prayer times change every day, vary significantly by latitude, and why a Muslim in Jakarta and a Muslim in Oslo have dramatically different prayer schedules even on the same day. Understanding the astronomical basis helps Muslims appreciate this system and explains why different apps sometimes show slightly different times for the same location.

The Five Salah Times and Their Definitions

Fajr (Dawn prayer): Begins at astronomical twilight when the sun is at a specific angle below the horizon, typically 15 degrees or 18 degrees depending on the calculation method, and the first hint of light appears in the east. Ends at Sunrise.

Dhuhr (Midday prayer): Begins when the sun crosses the local meridian (solar noon, the highest point in the sky that day). Exact time varies by longitude and time of year due to the equation of time.

Asr (Afternoon prayer): Begins when the shadow of an object equals its own length plus its noon shadow (Shafi'i method), or twice its length plus noon shadow (Hanafi method). This is why Hanafi Asr is always later than Shafi'i Asr.

Maghrib (Sunset prayer): Begins immediately at sunset when the sun's upper edge disappears below the horizon. All major schools agree on this definition.

Isha (Night prayer): Begins when the red twilight in the west disappears, when the sun is approximately 15-18 degrees below the horizon. This is the evening equivalent of Fajr's dawn calculation.

Why Prayer Times Differ by Location

Every location has a different solar noon time, different shadow change rates, and different sunrise and sunset times, all determined by latitude and longitude. At high latitudes above 45 degrees north (most of Europe), summer Isha can be extremely late or the sun may not reach the required angle below the horizon at all. Islamic scholars have developed several methods for high-latitude prayer times.

At low and mid latitudes, prayer times are more consistent year-round, though summer and winter Fajr and Isha can still differ by an hour or more.

Why Different Apps Show Different Times

Different organizations use slightly different twilight angles for Fajr and Isha:

University of Islamic Sciences Karachi (UISK): Fajr at 18 degrees, Isha at 18 degrees. This method is widely used in South Asia and by some communities elsewhere, and many local mosque timetables follow it.

Muslim World League (MWL): Fajr at 18 degrees, Isha at 17 degrees. Used widely in Europe and globally.

ISNA (North America): Both at 15 degrees.

Umm al-Qura (Saudi Arabia): Fixed 90-minute offset after Maghrib for Isha.

Many mosques publish their own timetable using one of these methods. If your app uses a different method, its Fajr and Isha times will differ slightly from your local mosque timetable, so choose the method your mosque follows.

Atmospheric Refraction and Elevation

Prayer calculations also account for atmospheric refraction, the bending of sunlight as it passes through the atmosphere. This adds approximately 2-3 minutes to visible sunrise compared to geometric calculation. Elevation above sea level also affects times, at higher altitudes, the horizon is effectively lower, so sunrise appears earlier and sunset later. Major prayer time algorithms include elevation correction.

Why Your Mosque's Adhan Sometimes Differs From the App

Even using the same calculation method, a mosque's announced time and an app's calculated time can differ by a few minutes, and this is normal rather than an error in either. Many mosques apply a small precautionary margin (ihtiyat), a few extra minutes added after the calculated Fajr start or subtracted before calculated Maghrib end, so that the congregation prays safely inside the window rather than exactly at the mathematical boundary, where a slight inaccuracy could mean praying a few minutes too early. Committees also sometimes round times to the nearest five minutes for a printed monthly timetable, while an app calculates the exact minute for that specific day.

If you notice a consistent gap of more than 5-10 minutes between your app and your local mosque, check first whether the app is using the same calculation method (UISK versus MWL versus another convention) and the same elevation setting, this explains the overwhelming majority of real discrepancies before assuming either source is wrong.

Choosing a method

Ask your local mosque which method it follows and use the same one in your app. Set your location as precisely as you can, because times shift slightly with longitude and latitude.