How the Prayer Times Are Determined

1 — Fajr: the true dawn

Fajr begins at al-fajr al-sadiq (the “true dawn”) — the first horizontal glow that spreads across the horizon — and ends at sunrise. It is distinguished from al-fajr al-kadhib (the “false dawn”), a vertical column of light that appears earlier and then fades. The Quran ties the fast and the prayer to this moment: “…until the white thread of dawn becomes distinct to you from the black thread” (2:187).

Astronomically, true dawn is when the sun is a fixed angle below the horizon and its light first reaches the sky. Calculators express this as a depression angle, commonly 18° (or 15°–19.5° depending on the method) below the horizon.

2 — Dhuhr: the sun leaves the zenith

Dhuhr begins just after the sun passes its highest point (the zenith, or zawāl) and starts to decline. The brief moment the sun is exactly overhead is a forbidden time for voluntary prayer; once it has clearly moved past, Dhuhr enters. In modern terms this is solar noon for your longitude plus a small margin, not clock 12:00.

3 — Asr: the shadow method (where the schools differ)

Asr is defined by the length of an object's shadow. Set aside the small shadow an object casts at noon (the “shadow at zawāl”). Then:

• Majority (Maliki, Shafi'i, Hanbali): Asr begins when an object's shadow equals its own length (plus the noon shadow).
• Hanafi: Asr begins when the shadow equals twice the object's length (plus the noon shadow) — so the Hanafi Asr starts later.

This is a genuine, well-known difference of the classical schools; both are valid positions traced to the reports on the Prophet ﷺ. Many calculators offer a “Standard” and a “Hanafi” Asr precisely for this reason.

4 — Maghrib: sunset

Maghrib begins at sunset — when the sun's disc has fully disappeared below the horizon — and this is also when the fasting person breaks the fast. It is the simplest of the five to observe directly. (A small correction for atmospheric refraction and the observer's elevation is applied in precise calculation.)

5 — Isha: the twilight disappears

Isha begins when the lingering red glow of dusk (al-shafaq) fades from the western sky and full night sets in. As with dawn, this usually maps to a solar depression angle — 15° (ISNA) up to 17° (Muslim World League), depending on the method. Umm al-Qura is the exception: instead of an angle, it fixes Isha at 90 minutes after Maghrib (120 minutes during Ramadan).

From the sky to the calculator

Every classical sign above corresponds to a measurable position of the sun, so a calculator reproduces the same rulings with geometry — using your latitude, longitude, date, and a chosen calculation method (which simply fixes the Fajr/Isha angles and the Asr shadow ratio):

Common methods (Muslim World League, ISNA, Umm al-Qura, Egyptian Authority) mostly differ only in the Fajr/Isha angles they use — Umm al-Qura's Isha is the one exception, computed as a fixed time offset from Maghrib rather than an angle — which is why the same location can show times a few minutes apart between apps. In far-northern/southern latitudes where twilight may not end before dawn in summer, methods apply an approximation (e.g. “nearest latitude” or “middle of the night”).