Converting Hijri to Gregorian dates: the rule, worked examples and a month table

People ask for a formula that converts Hijri to Gregorian the way metres convert to feet. An exact formula of that kind does not exist, and the reason is not a gap in mathematics but the nature of the moon. You can still reach a close answer with mental arithmetic in seconds, then pin the exact day down with a table.

Why there is no simple formula

A lunar month averages about 29.53 days, and a day based calendar cannot use a fraction of a day, so months alternate between 29 and 30. A Hijri year runs 354 or 355 days, about 11 days shorter than a Gregorian year.

Three consequences explain nearly every conversion mistake:

• Hijri dates move forward through the Gregorian year by about 11 days annually, which is why Ramadan drifts from summer to winter over three decades.
• One hundred Gregorian years correspond to about 103 Hijri years.
• Any direct formula is sometimes off by a day or two, because it works with an average rather than an observed crescent.

The approximate mental rule

Gregorian to Hijri: (Gregorian year minus 622) multiplied by 1.0307.

Hijri to Gregorian: (Hijri year multiplied by 0.97) plus 622.

Example: 2026 minus 622 is 1404; multiplied by 1.0307 gives about 1447. In reverse: 1447 times 0.97 is 1403.6; plus 622 gives about 2026. The rule gives you the year accurately enough for general reference, not the day and month. For those use the Hijri date converter.

Three systems, three answers

This is why two websites can disagree about today:

1. Moon sighting: the month begins when the crescent is seen, so it varies by horizon and official decision. An accurate yearly calendar cannot be printed from it in advance.
2. Umm al-Qura: an astronomical calculation used administratively in Saudi Arabia, and the one this platform displays.
3. The tabular calendar: an arithmetic system on a thirty year cycle, common in software libraries, which differs by one day on many dates.

The differences between these systems are covered in detail in why Hijri dates differ between your app and your country.

Worked examples under three systems

Notice how the day shifts by one between systems for the same Gregorian instant:

The lesson matters more than the numbers: a one day gap is normal. If your Hijri birth date differs between two documents, each authority most likely used a different system.

Gregorian start of each month of 1448 AH

By the Umm al-Qura calculation, which is what the Hijri calendar page displays. Devotional months may start a day earlier or later depending on the sighting announced in your country.

From that table you can already see that the first fasting day of 1448 falls around 8 February 2027, Eid al-Fitr around 9 March 2027, and the Day of Arafah around 15 May 2027. See the Ramadan page for seasonal detail.

The Hijri months and their names

Muharram, from the prohibition of fighting in it; Safar, from homes emptying for travel; Rabi al-Awwal and Rabi al-Thani, the spring season; Jumada al-Ula and Jumada al-Akhirah, from water freezing in the cold; Rajab, from veneration; Shaban, from dispersing in search of livelihood; Ramadan, from intense heat; Shawwal, from camels raising their tails; Dhul Qadah, from sitting out of battle; Dhul Hijjah, the season of Hajj.

Four are sacred: Dhul Qadah, Dhul Hijjah, Muharram and Rajab, three consecutive and one apart.

Common conversion mistakes

• Subtracting 579 from the Gregorian year is a widespread shortcut that is a full year wrong in about half of all cases, because it ignores the difference in year length.
• Treating every month as 30 days, which accumulates into a week of error within a year.
• Converting a birth time after midnight while the Hijri day begins at sunset the previous evening, so a birth after sunset falls on the next Hijri day.
• Mixing sighting with calculation for Ramadan and Eid, then accusing one of being wrong.

Frequently asked questions

Is there an exact formula for converting Hijri dates?

No formula is exact, because a lunar month is not a whole number of days and devotional months depend on the sighting of the crescent. The approximate formula gives the year reliably, while the day and month need a calculated table such as Umm al-Qura.

How do I convert a Gregorian year to Hijri mentally?

Subtract 622 from the Gregorian year, then multiply by 1.0307. For example, 2026 minus 622 is 1404, and 1404 times 1.0307 is about 1447 AH.

Why does my Hijri birth date differ between two documents?

Usually because each authority used a different system: Umm al-Qura, the tabular calendar, or local sighting. The gap is normally a single day, and occasionally a month when the birth fell at the very end of a month.

When does the day start in the Hijri calendar?

At sunset, not at midnight. Anything after sunset counts as the next Hijri day, which explains a one day difference when converting evening birth times.

How many Gregorian years match one hundred Hijri years?

About 97, because the Hijri year is roughly 11 days shorter. That is why Hijri dates gain on Gregorian ones over the centuries.

Putting this to use

Use the approximate rule for a fast estimate of the year, use the date converter to fix the exact day and month, and remember that a one day gap between two sources is expected rather than wrong. If you calculate zakat on a lunar year, fix your Hijri due date once and then use the zakat calculator each year.