Hijri age: the Umm al-Qura calendar and the eleven-day year

The Hijri calendar is purely lunar. Twelve lunar months come to 354 or 355 days, about eleven short of a solar year, and nothing is ever inserted to make up the difference. Two consequences follow, and between them they are most of what this page is about: a Hijri age runs ahead of a Gregorian one, and a Hijri birthday moves backwards through the seasons.

Why the two counts diverge

Almost every other calendar on this site is solar or lunisolar — tied to the seasons either directly, like the Gregorian and Solar Hijri calendars, or by inserting a thirteenth month when the drift gets too large, like the Hebrew and Chinese ones. The Hijri calendar does neither. Its year is twelve lunar months and no more, so it slips against the solar year at a steady eleven days, and a Hijri date carries no information about the season it falls in.

Eleven days a year compounds into a whole year roughly every thirty-three. Someone who has lived 33 Gregorian years has lived about 34 Hijri ones, and the gap keeps widening.

A Hijri birthday walking backwards

The other consequence is easier to feel. Take a birth on 15 May 1990, which is 20 Shawwal 1410 AH. That Hijri date recurs every Hijri year, and each time it lands about eleven days earlier in the Gregorian one. Over the twenty years below it crosses from June to November, through every season on the way.

This is why a Hijri birthday and a Gregorian one are two different observances rather than two spellings of the same day, and why Ramadan is sometimes a winter month and sometimes a summer one for the same person in the same lifetime.

The twelve months

Worked examples

Ages as they stand on 20 August 2026 in Riyadh, computed when this page was built by the same module the calculator uses. The Gregorian column is there for contrast: it is the same two instants, counted by a different calendar.

The next birthday is a date, not an average

A Hijri year has no fixed length, so the next Hijri birthday cannot be found by adding one to the last. This site looks the date up in the calendar instead: it takes the month and day of the Hijri birth date and finds the next Hijri year in which that combination occurs. Where it does not occur — a birth on the 30th of a month that has 29 days in the year being asked about — the anniversary is observed on the last day of that month, and the table above says so in the row it applies to rather than adjusting quietly.

Counting from the Hijra

Year 1 of the calendar is the year of the Hijra, the migration of the Prophet Muhammad and his followers from Mecca to Medina, in 622 CE. Dates are written AH, for anno Hegirae. Because the Hijri year is shorter, the two era numbers converge very slowly: 1400 AH began in 1979 CE, and the gap of about 579 years at that point narrows by roughly one year every thirty-three.