Hijri vs Gregorian Calendar: Conversion Guide (2026)

What the Hijri calendar is

The Hijri calendar, also called the Islamic calendar, is a lunar calendar of twelve months that counts its years from the migration, the Hijra, of the Prophet Muhammad from Mecca to Medina in 622 CE. Its months are Muharram, Safar, Rabi al-Awwal, Rabi al-Thani, Jumada al-Ula, Jumada al-Akhira, Rajab, Shaban, Ramadan, Shawwal, Dhul-Qadah and Dhul-Hijjah. Because a lunar month is the time from one new moon to the next, about 29.5 days, the twelve months add up to roughly 354 days, about 11 days shorter than the Gregorian year.

That 11-day gap is the defining feature of the Hijri system. Religious obligations tied to it, such as Ramadan, the Hajj pilgrimage and the two Eids, move about 11 days earlier in the Gregorian calendar every year, so over roughly 33 years each Islamic date has passed through every season. The calendar governs worship dates everywhere, and it is also the official civil calendar in Saudi Arabia, where salaries, contracts and identity documents carry Hijri dates alongside or instead of Gregorian ones.

A Hijri date is written with the letters AH. The Gregorian year 2026 spans most of the Hijri years 1447 and 1448, which is why a converter can return two different Hijri years for two days in the same Gregorian year: the Islamic new year falls around mid-year, not on 1 January. This split surprises no one in the Gulf, but it catches out anyone who expects a one-to-one match between year numbers.

Umm al-Qura versus local moon sighting

Two ways of fixing the start of an Islamic month coexist. The Umm al-Qura calendar, used by Saudi Arabia for civil purposes, fixes the months by astronomical calculation in advance, so it is predictable and identical everywhere. Traditional practice, by contrast, starts the month when the new crescent moon is actually sighted, which depends on weather, horizon and the ruling of local religious authorities.

The two methods agree most of the time but can differ by one day, and neighboring countries sometimes start Ramadan or celebrate Eid on different days as a result. Date converters, including the one on this site, follow a calculated calendar, so their output is the calculated date. If your community follows local sighting, the actual religious date may fall a day earlier or later than the converted one. Treat converted dates for worship as accurate to about a day, and confirm the start of a month with a local authority when it matters.

For paperwork the situation is simpler: civil documents follow the official calculated calendar of the country that issued them, so conversions for visas, contracts and records are exact within that convention. The one-day ambiguity is a religious-calendar question, not a data question.

The 30-year cycle and month lengths

In the calculated Islamic calendar, months alternate between 30 and 29 days. The odd-numbered months, Muharram, Rabi al-Awwal, Jumada al-Ula, Rajab, Ramadan and Dhul-Qadah, have 30 days, and the even-numbered months have 29, so a normal year holds 354 days. To keep the count aligned with the moon over the long term, 11 of every 30 years are leap years of 355 days, in which the last month, Dhul-Hijjah, takes 30 days instead of 29. The leap years fall on fixed positions of each 30-year cycle: years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26 and 29.

A full cycle of thirty years therefore holds 30 times 354 plus 11 extra days, which is 10,631 days, an average of about 354.37 days per year. The Umm al-Qura calendar is more precise than this fixed pattern because it derives month starts from astronomical new moon calculations rather than the rigid cycle, and it can place a month start one day away from the tabular result. That is also why two converters can occasionally disagree by a day: they may implement different calculated calendars, and each is internally consistent with itself. The table lists the twelve months and their lengths in a normal year.

How conversion works computationally

Every date in either calendar is just a count of days from that calendar’s starting point, called its epoch. The Hijri epoch is 1 Muharram of the year 1 AH, which corresponds to 16 July 622 CE in the astronomical reckoning that most algorithms use. Converting means turning the given date into a plain day number, such as a Julian day number, applying the arithmetic of the target calendar, and reading a year, month and day back out. Nothing mystical happens in between; it is date arithmetic over two different counting rules.

The Hijri side of that arithmetic uses exactly the month lengths and the 30-year cycle described above, so it is exact for a calculated calendar. The residual uncertainty is observational, not mathematical: the real new moon becomes visible in some places before others, and religious authorities confirm sightings. This is why the same converter output can correspond to two real-world dates in different countries, and why serious converters state which convention they implement rather than leaving users to guess.

A worked conversion makes the mechanics concrete. Take 18 February 2026 and convert to Hijri on the Umm al-Qura convention: the day count from the Hijri epoch lands on 1 Ramadan 1447, the expected first day of fasting. Reversing the direction, 10 Dhul-Hijjah 1447 reads back as 27 May 2026, the expected day of Eid al-Adha. Every conversion reduces to that same operation, whatever the direction, and the converter applies it instantly for any pair of dates you enter, so a birth date, a contract date and a deadline all go through the identical pipe.

Key Islamic dates in 2026 and 2027 (approximate)

Because month starts depend on sighting, any list of Islamic dates for a coming year is approximate. The table gives the expected Gregorian dates of the main events on the calculated Umm al-Qura calendar, and each one may shift by a day with local moon sighting. Confirm the exact day with your local authority before planning worship, travel or events.

Note the drift from one year to the next. Ramadan 1447 begins around mid-February 2026, while Ramadan 1448 is expected around a week into February 2027, roughly 11 days earlier in the Gregorian calendar. The same shift applies to every other Islamic date, which is why a Hijri date has no fixed Gregorian position: it must be converted for the specific year in question, and re-checked the following year.

Why ages differ between the two calendars

Because a Hijri year averages about 354.37 days against 365.24 for the Gregorian year, Hijri ages accumulate about 3 percent faster. Multiply a Gregorian age by about 1.0307 to estimate the Hijri age. A person whose Gregorian age is exactly 30 has a Hijri age of about 30 years and 11 months, and the gap widens to a full year roughly every three decades of life.

For a concrete case, someone born on 1 January 2000 reaches a Gregorian age of 26 years and about 9 months on 25 September 2026, while their Hijri age is about 27 years and 5 months. On official Saudi forms that ask for age in Hijri years, the completed Hijri age is 27, one year more than the Gregorian 26. This is the single most common surprise when people compare documents issued in different systems, and the age calculator resolves it by letting you switch the calendar before computing.

The practical rule is to always match the calendar of the birth date to the calendar of the question. Convert a Hijri birth date before mixing it with Gregorian ages, or the reverse, and never subtract year numbers taken from the two systems directly. A one-year mismatch that looks like an error is usually just two calendars answering two different questions.