Why Does the Date of Ramadan Change Every Year?

Anyone born in the 1980s remembers Ramadan in cold weather and short days. Anyone born after 2010 has only known summer Ramadan. They fast the same month; the calendar is moving beneath them.

The rule in one sentence

Ramadan advances about eleven days earlier in the Gregorian calendar every year — no more, no less, because the lunar year is shorter by exactly that much.

If Ramadan begins on 10 March this year, it begins around 28 February next year, and around 17 February the year after.

A calculation you can do in your head

Subtract eleven days for each year ahead. For longer spans, multiply the number of years by eleven and subtract the total from today's date.

Where will Ramadan be in ten years? Ten times eleven is one hundred and ten days — roughly three and a half months earlier than today's date.

This is an approximation, off by a few days, because lunar months alternate between twenty-nine and thirty. Exactness requires a tabular calculation.

The thirty-three-year cycle

Thirty-three years times eleven days is 363 days — very nearly one full Gregorian year.

Which means Ramadan returns to the same position in the Gregorian calendar roughly every thirty-three years. Someone who fasted Ramadan in January at twenty will fast it in January again at fifty-three.

Along the way it passes through every season: winter, then autumn, then summer, then spring, and back again.

What follows in practice

The length of the fasting day changes dramatically. A summer Ramadan in northern latitudes can mean twenty hours or more of daylight; a winter one in the same place may mean under ten.

This is why jurists have devoted so much attention to polar and near-polar regions, where at certain times the sun may not set at all.

It also explains why Ramadan holidays cannot be fixed in a Gregorian school calendar — they move every year.

A note on calculation and sighting

Everything above uses the tabular Hijri calendar. In most Muslim countries, however, the start of Ramadan is announced on the basis of sighting the crescent, which may fall a day earlier or later than the calculation.

Treat any advance calculation as a precise estimate, not an announcement. The announcement comes from the relevant authority in your own country.

Ramadan does not move. The Gregorian calendar slides beneath it — the month stays fixed in the sky, and the seasons pass underneath.

Sources: NASA synodic month data; the tabular Hijri algorithm; Islamic Fiqh Academy rulings on fasting times at high latitudes