How Islamic Prayer Times Are Calculated
Islamic prayer times are not guessed or estimated — they are computed from the sun's exact position using precise trigonometric formulas. Here is exactly how it works, why different apps show different times, and which method most US mosques use.
The foundation: the sun's position defines every prayer
Every Islamic prayer time is derived from the sun's altitude angle above (or below) the horizon at a specific geographic location. The five prayers map to five distinct solar positions:
- Fajr — when the sun reaches a specific angle below the eastern horizon (before dawn)
- Sunrise — when the upper limb of the sun crosses the horizon (ends Fajr window)
- Dhuhr — when the sun reaches its highest point in the sky (solar noon)
- Asr — when the shadow of an object reaches a specific length relative to itself
- Maghrib — when the sun fully sets below the horizon
- Isha — when the sun reaches a specific angle below the western horizon (after twilight)
Four of these times — Dhuhr, Sunrise, Maghrib, and Asr — are agreed upon by all scholars and all calculation methods. The differences you see between apps are almost entirely in Fajr and Isha.
Your current prayer times are calculated using these exact formulas — try the auto-detect tool on the homepage to see Fajr and Isha for your precise location today.
The math: how the sun's position is computed
Given a latitude, longitude, and date, the sun's altitude at any moment can be calculated using the following inputs:
- Solar declination — the angle between the sun and the Earth's equatorial plane, which changes throughout the year (ranging from −23.5° in December to +23.5° in June)
- Hour angle — how far the sun has traveled from its noon position, measured in degrees
- Observer's latitude — determines how high the sun rises and how long it stays above the horizon
The core formula for solar altitude is:
sin(altitude) = sin(lat) × sin(dec) + cos(lat) × cos(dec) × cos(hour_angle)
For Fajr and Isha, we invert this — we specify the target altitude angle and solve for the hour angle (i.e., what time does the sun reach that angle). This is where method differences appear.
Why Fajr and Isha times differ between methods
Fajr begins at true dawn (Subh Sadiq) — the moment the first horizontal whiteness appears on the eastern horizon. Astronomically, this corresponds to a specific angle of the sun below the horizon. Different scholarly traditions interpreted this angle differently based on observations made centuries ago at different latitudes.
The result is that major calculation methods use different threshold angles:
| Method | Fajr Angle | Isha Angle | Common use |
|---|---|---|---|
| ISNA | 15° | 15° | United States (most common) |
| Muslim World League | 18° | 17° | Europe, Far East, parts of USA |
| Egyptian General Authority | 19.5° | 17.5° | Africa, Syria, Lebanon, Malaysia |
| University of Karachi | 18° | 18° | Pakistan, Bangladesh, India, Afghanistan |
| Umm Al-Qura (Makkah) | 18.5° | Fixed 90 min after Maghrib | Saudi Arabia |
| Tehran | 17.7° | 14° | Iran, some Shia communities |
A higher Fajr angle means the sun needs to be further below the horizon — which means Fajr is calculated earlier. So ISNA (15°) gives a later Fajr than Egyptian (19.5°). This can be 10–20 minutes earlier or later depending on your latitude and the season.
How Asr is calculated (and why it's different)
Unlike Fajr and Isha, Asr is not based on the sun's angle below the horizon — it's based on the length of shadows. The scholarly debate here is between two madhabs:
- Shafi'i, Maliki, Hanbali:Asr begins when an object's shadow equals its own height (shadow factor 1). This produces an earlier afternoon prayer.
- Hanafi:Asr begins when an object's shadow is twice its height (shadow factor 2). This can be 30–60 minutes later, especially in summer.
The practical implication: if you follow the Hanafi school and an app shows ISNA times with Shafi'i Asr, your Asr time will be wrong. Always verify which madhab your app uses. On Prayer Times Near Me, you can switch the madhab in the Settings panel on any city page.
High-latitude challenges
In cities at extreme latitudes (above 48°N or below 48°S), astronomical twilight in summer can last all night — meaning the sun never reaches the Fajr or Isha threshold angles. In these cases, calculation methods use special rules:
- Middle of the Night: Isha is set to midnight
- 1/7th of the Night: Split the night into sevenths
- Angle-Based: Use the closest day where twilight fully disappears
- Nearest Latitude: Use the prayer times of the nearest location without this problem
Minneapolis (44.97°N) and cities further north occasionally encounter this in deep summer. The adhan.js library we use handles this automatically.
How to know which method your mosque uses
Most US mosques use ISNA, but many South Asian-majority mosques use the Karachi (Hanafi) method. The simplest way: ask your mosque which calculation method they announce times by, or compare our times for your city against your mosque's posted schedule — if they differ, switch methods in the Settings panel until they match.
Find your city's prayer times computed with your mosque's exact method on the city pages directory. Settings panel lets you switch methods instantly.
The accuracy of modern calculation
Modern prayer time calculations are extremely accurate — within 1–2 minutes of physical observation under clear conditions. The main source of variation between apps is not the math but the method choice and elevation adjustments. Apps at sea level and apps with elevation correction will show slightly different Maghrib times for mountain cities.
We cross-validate our times against IslamicFinder.org and MuslimPro for each major US city. Our times consistently match within 1 minute when using the same method. If you find a larger discrepancy, it's almost always a method mismatch — check your settings first.
Frequently Asked Questions
Why do different apps show different prayer times?
Different apps use different calculation methods. The ISNA method (used by most US mosques) differs from the Muslim World League or Egyptian methods by using different angles for determining Fajr and Isha. Even 1–2 degrees of difference produces noticeably different times.
Which prayer time calculation method is most accurate?
All major methods are astronomically correct — they use the same trigonometry. The difference is in the threshold angle, which is a matter of scholarly interpretation. The "most accurate" method is whichever your local mosque or Islamic authority follows.
Are prayer times the same every day?
No. Prayer times shift every day as the sun's position changes with Earth's orbit. In summer, Fajr is earlier and Isha is later; in winter, the reverse. The daily shift is typically 1–3 minutes. Monthly prayer calendars (available on every city page) let you plan ahead.
What is the most common prayer calculation method in the US?
ISNA (Islamic Society of North America) is the most widely used method among US mosques, using Fajr angle 15° and Isha angle 15°. Most Islamic apps default to ISNA for US users — including Prayer Times Near Me.