What is the Hijri calendar?
The Hijri calendar is the Islamic lunar calendar. It started counting from the Hijrah - the migration of the Prophet Muhammad ﷺ from Mecca to Medina in 622 CE. A Hijri year contains 12 lunar months totaling about 354 days, roughly 11 days shorter than a Gregorian year. The calendar is the religious calendar of the Muslim world and the official civil calendar of Saudi Arabia.
Why convert between Gregorian and Hijri?
Saudi national IDs, birth certificates, school records, and many government documents are issued in Hijri. International airlines, banks, foreign universities, and most non-Saudi institutions use Gregorian. People constantly need to convert in both directions - to fill out a visa form, register for a course, prove their age in another jurisdiction, or calculate religious dates like Ramadan and Hajj in advance.
How the conversion works
Both calendars can be expressed as a Julian Day Number (JD) - a continuous count of days since a fixed reference point in 4713 BC. We first convert your Gregorian date to JD using Meeus's astronomical algorithm, then convert that JD into the Hijri date using the tabular Islamic calendar algorithm. The day of the week is preserved automatically - a Tuesday is a Tuesday regardless of which calendar you label it with.
Umm al-Qura vs Tabular Hijri
Saudi Arabia uses the Umm al-Qura calendar - an observation-based calendar where the start of each lunar month is determined by physically sighting the new moon (or by precise astronomical prediction matching expected sighting). The tabular Islamic calendar we use here is a fixed-arithmetic calendar that approximates Umm al-Qura within ±1 day. For everyday use the difference is negligible; for legal documents, verify against the official Umm al-Qura source.
Why Ramadan moves through the Gregorian year
Because a Hijri year is about 11 days shorter than a Gregorian year, every Hijri date shifts ~11 days earlier in the Gregorian calendar each year. Ramadan moved from June in 2014 to March in 2024 and will move into February by the late 2020s. Over 33 years a Hijri month rotates through all four Gregorian seasons. This calculator handles the math so you don't have to.
Supported date ranges and precision
We support Gregorian dates from 1900 to 2100 in this widget. The underlying algorithm works for any date in history but everyday use cases - birth dates, ID dates, planning religious holidays - fall in that range. Precision is ±1 day vs Umm al-Qura. The day of the week is exact.
Frequently asked questions
We use the tabular Islamic calendar - a fixed arithmetic calendar that approximates the observational Umm al-Qura calendar used in Saudi Arabia. The difference is at most one day, on dates when the actual new moon sighting and the arithmetic prediction land on different sides of midnight. For legal documents, cross-check with the official Umm al-Qura source.
Because a Hijri year is about 354 days - roughly 11 days shorter than a Gregorian year. So every Hijri date, including the start of Ramadan, shifts about 11 days earlier on the Gregorian calendar each year. Over 33 Gregorian years, Ramadan rotates through every season.
Yes. The arithmetic algorithm works equally well for past or future dates. For dates close to today the conversion is reliable; for far-future religious calendar planning (years ahead), expect the same ±1 day Umm al-Qura tolerance.
No. Wednesday is Wednesday regardless of whether you label it 12 Rabi' al-Thani 1446 or 15 October 2024 - it's the same physical day. We display the weekday so you can verify the conversion at a glance.
Lunar months alternate between 29 and 30 days, averaging 29.53 days each. Twelve lunar months give 354 days in a regular year and 355 in a leap year (the 11 leap years out of every 30 in the tabular calendar). The Gregorian calendar is solar - it tracks the Earth's orbit around the Sun - so its 365.25-day year is longer.
Sources
- Umm al-Qura Calendar (official Saudi calendar)— King Abdulaziz City for Science and Technology (KACST)
- Tabular Islamic Calendar - Astronomical Algorithms (2nd ed.)— Jean Meeus
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