Ramadan Fasting Hours Calculator

How it works

Solar noon = 12:00 − 4 × longitude − equation of time + UTC offset; hour angle H for altitude −a: cos H = (sin(−a) − sin φ sin δ) ÷ (cos φ cos δ); Fajr = noon − H(18°)/15 h, Maghrib = sunset = noon + H(0.833°)/15 h; fast = Maghrib − Fajr

The fast runs from true dawn — when the first light appears while the sun is still well below the horizon — to sunset, so it is always longer than the daylight hours, and its length depends on latitude and season: about 13 hours in Cairo in spring, 18 or more in London in June, under 11 in Buenos Aires in July. Dawn is defined astronomically by how far the sun sits below the horizon; 18° is the classical and most widespread figure, with 15° used across North America and 12° by some British timetables, differences that move suhoor by 15–30 minutes. Sunset needs no convention beyond refraction. Above roughly 48° latitude the sun never gets 18° below the horizon on summer nights, and scholars prescribe alternative rules — following the nearest date or city where it does, Mecca’s times, or a fixed share of the night.

Worked example

London (51.51° N) on 27 September with the offset left at 0 (GMT): Fajr at 18° falls at 04:02 and sunset at 17:48, a fast of 13 h 46 min — almost two hours longer than the 11 h 53 min of daylight (add an hour to both times while BST is in force); the 15° convention would allow suhoor about 20 minutes later. In late June the same city fasts over 18 hours, in December under 10.

Frequently asked questions