How prayer times are calculated

Before sunrise the sky brightens while the Sun is still below the horizon. Astronomers call the moment it passes 18° below the horizon “astronomical twilight”, and 12° “nautical twilight”. Conventions use an angle between 12° and 20° for Fajr, and between 12° and 18° for Isha. The diagram shows the Sun’s height in Paris from midnight to noon: in summer the Sun never sinks to 18°.

The gap between two angles depends on latitude and season: in Paris, one degree is worth 7 to 8 minutes in winter and much more in summer. Between 12° and 18°, the difference ranges from three quarters of an hour to more than an hour and a half. The convention therefore weighs a hundred times more than the accuracy of the astronomical calculation.

The further north, the less the Sun sinks below the horizon on summer nights. At midnight its height is −(90° − latitude − declination): at the solstice it does not pass 18° below the horizon north of 48.6° (Strasbourg), nor 15° north of 51.6°, nor 12° north of 54.6°. On those nights, 18° dawn does not exist in the astronomical sense. The table counts those nights for a few cities.

Conventions fill those nights with a fallback rule:

• middle of the night: Fajr cannot be earlier than the middle of the sunset–sunrise interval, nor Isha later;
• one seventh of the night: Fajr at the earliest one seventh of the night before sunrise, Isha at the latest one seventh after sunset;
• angle-based fraction: a share of the night equal to the angle divided by 60 (18° gives 30% of the night);
• Moonsighting Committee seasonal durations: Fajr a number of minutes before sunrise that depends on latitude and day of the year (75 minutes plus a seasonal term), Isha likewise after sunset;
• the times of the nearest latitude where the angle exists (aqrab al-bilad) or of the nearest day when it exists (aqrab al-ayyam), mostly beyond the polar circle.

These limits apply even when the angle exists: the Fajr used is the later of the two, the Isha the earlier. This is why two timetables that both say “18°” can differ in summer.

Each country follows a convention published by a religious or astronomical authority or, failing that, a common practice. The method applied by default on the site’s pages is shown below; every city page shows the other methods side by side.

The 2026 timetable published by the Grand Mosque of Paris is reproduced to the minute by the following rule:

• Fajr: sunrise minus the seasonal durations of the Moonsighting Committee (the 18° angle is never used in Paris, as the seasonal limit is always later);
• sunrise: astronomical sunrise (−0.833°);
• Dhuhr: solar noon plus 5 minutes;
• Asr: one shadow length;
• Maghrib: sunset plus 3 minutes;
• Isha: sunset plus 90 minutes.

This method is applied by default to cities in France, Belgium, Switzerland and Luxembourg. It stays defined all year up to 55° latitude (Lille and Brussels included), where the 18° angle is missing in summer, and does not delay Fajr the way the 12° angle does. French city pages also show the 12°, 15° and 18° methods.

Times are rounded for safety: the start of each prayer to the next minute, sunrise to the previous minute, except for methods that reproduce an official timetable, which keep its rounding. Time zones and clock changes come from the system’s time zone database (Morocco has stayed on GMT all year since 20 September 2026).