How Old Am I in Hijri Years? A Step-by-Step Method

The question surfaces when filling in an official form, or simply out of curiosity: how old am I in the Hijri calendar? The answer takes longer than subtracting two numbers, because the two calendars are not measuring the same thing.

The basic rule: two years of different lengths

The Gregorian year is solar, built on the Earth's orbit around the Sun: roughly 365 and a quarter days. The Hijri year is lunar, built on twelve complete orbits of the Moon around the Earth: roughly 354 days. The gap is about eleven days every year.

That small gap accumulates. After three years it is nearly a full month. After thirty-three Gregorian years it is a complete extra Hijri year. This is why your Hijri age is always higher than your Gregorian age, and can never be lower.

The quick approximation

For a rough figure, multiply your Gregorian age by 33 and divide by 32. Someone aged 32 in Gregorian years is about 33 in Hijri years; someone aged 64 is about 66.

The method gives whole years only and is off by days or weeks. Fine for conversation, not for paperwork.

The exact method: three steps

Step one: convert your Gregorian birth date to its Hijri equivalent. Someone born on 1 January 2000 was born on 24 Ramadan 1420 AH.

Step two: find today's date in the Hijri calendar.

Step three: subtract the first from the second exactly as you would subtract Gregorian dates — year from year, month from month, day from day, borrowing where needed.

The one difference lies in the borrowing. In the Gregorian calendar you borrow thirty or thirty-one days. In the Hijri calendar you borrow twenty-nine or thirty, because lunar months alternate in length with the Moon's cycle.

Why so many calculators get it wrong

Many online tools compute a Hijri age by dividing elapsed days by 354. That yields the number of lunar years, but not accurate months and days, because lunar months are not equal.

Others make a deeper mistake: they use one algorithm to convert Gregorian to Hijri and a different, incompatible one for the reverse. The two directions then disagree, sometimes by more than a full year. The test that exposes it takes ten seconds — convert a date one way, convert the result back, and see whether you land on the date you started from. If you do not, the tool is broken.

Calculation and sighting

One distinction matters. The tabular Hijri calendar is arithmetic: month lengths follow a fixed mathematical rule, which is why official systems and software use it — it can be computed centuries ahead.

But in many Muslim countries the start of a Hijri month is announced by sighting the crescent, which depends on location and atmospheric clarity. A sighted month may begin a day before or after the calculated one.

So your calculated Hijri birth date may differ by a day from the one printed on your official documents. That is not an error in the arithmetic; it is a difference in which authority is being followed — and for official purposes, the document is the one that counts.

Your Hijri age is not a second age. It is the same span of life measured with a different ruler — the Moon's, instead of the Sun's.

Sources: al-Biruni, "The Remaining Signs of Past Centuries"; standards of the Islamic Fiqh Academy on the Hijri calendar; the tabular (Kuwaiti) Hijri algorithm