Calculation methods, explained.

What is a calculation method?

Five of the daily prayers — Fajr, Dhuhr, Asr, Maghrib, and Isha — are tied to specific astronomical conditions. Dhuhr, Asr, and Maghrib are reasonably uncontroversial: Dhuhr begins shortly after solar noon, Maghrib at sunset, and Asr at a defined shadow length. Fajr and Isha, however, are tied to the angle of the sun below the horizon during dawn and dusk twilight — and the precise angle adopted varies by tradition.

A "calculation method" is a packaged set of these angles plus a few related parameters (like how to handle the high-latitude regions where twilight may not end before dawn begins). WhiskAI uses two methods:

Muslim World League (UK)

Founded in 1962 in Mecca, the Muslim World League (MWL) is one of the largest international Islamic non-governmental organisations. Its prayer-time convention is the most widely adopted standard worldwide and is used across British mosques.

• Fajr angle: 18° below horizon
• Isha angle: 17° below horizon
• Asr school: Shafi'i (standard) by default

The 18° Fajr angle reflects the moment when the eastern sky begins to lighten with true dawn. In Britain's high latitudes, this can produce notably early Fajr times in summer.

Islamic Society of North America (US)

The Islamic Society of North America (ISNA), founded in 1981 and headquartered in Plainfield, Indiana, is the largest umbrella body for Muslim communities in the United States. The ISNA convention is the standard used by ISNA-affiliated mosques, ICNA, and most major American Islamic centres.

• Fajr angle: 15° below horizon
• Isha angle: 15° below horizon
• Asr school: Shafi'i (standard) by default

The tighter ISNA angles produce slightly later Fajr and earlier Isha times than MWL — typically 15 to 25 minutes of difference at temperate latitudes, with the difference growing in extreme summers.

Asr: Shafi'i versus Hanafi

Asr time depends on shadow length. The Shafi'i, Maliki, and Hanbali schools (sometimes called the "standard" school) consider Asr to begin when an object's shadow equals its own height plus the noon shadow length. The Hanafi school holds that Asr begins when the shadow equals twice the object's height plus the noon shadow.

In practical terms, the Hanafi Asr falls 50 to 90 minutes later than the standard Asr. WhiskAI defaults to the standard (Shafi'i) calculation but offers a Hanafi override on each city page via the calculation toggle.

Why we don't use other methods

Aladhan supports more than a dozen calculation methods including the Egyptian General Authority of Survey, the University of Islamic Sciences (Karachi), the Institute of Geophysics (Tehran), and several others. These are used by particular mosques and regions. WhiskAI defaults to MWL and ISNA because they are the most widely-adopted conventions in the regions we cover, and because consistency across cities allows like-with-like comparison. Where your local mosque follows a different convention, defer to its published times.