Hijri Calendar and Umm al-Qura: Accurate Hijri

You write a contract date in Hijri, a colleague converts it on another website, and a different day comes up. Or a client asks about the expiry date of a residence permit or licence recorded in Hijri, and you need its Gregorian equivalent quickly. Or you’re building a website for a Saudi organisation and want to show both dates correctly. The Hijri calendar is part of daily business in Saudi Arabia and the Gulf, and understanding how it’s calculated prevents small errors that can be costly in contracts and deadlines.

Hijri calendar basics

A lunar calendar: each month starts with the new crescent and lasts 29 or 30 days.
The Hijri year has 12 months and 354 or 355 days — about 11 days shorter than the Gregorian year.
The result: Hijri occasions (Ramadan, Eid) move about 11 days earlier each Gregorian year, cycling through all seasons in about 33 years.
The Hijri day traditionally begins at sunset, while most digital systems treat it as starting at midnight like the Gregorian day.

What is the Umm al-Qura calendar?

Umm al-Qura is the official Hijri calendar used in Saudi Arabia for civil and administrative purposes. It’s calculated astronomically in advance according to set criteria for the start of each month, so dates can be known years ahead — which is what contracts, systems and schedules need.

It’s also the calendar built into most modern systems as “islamic-umalqura”, used by browsers and operating systems when the Hijri calendar is selected with Saudi settings. Our Hijri date converter uses this calendar directly from the browser’s engine, with no hand-made tables that could be wrong.

Why is the Hijri date sometimes a day off?

This is the most frequent question, and the reasons are clear:

1. Umm al-Qura vs. moon sighting

The start of religiously significant months — especially Ramadan, Shawwal and Dhu al-Hijjah — is announced based on sighting the crescent. The sighting can differ from Umm al-Qura’s advance calculation by a day. So the calendar suits contracts and schedules, while religious occasions follow the official announcement.

2. Different Hijri calendars

Several calculation methods exist, including the “tabular” calendar based on a fixed arithmetic cycle, and calendars adopted by other countries. A site using a tabular calendar may give a different day from Umm al-Qura.

3. Country differences

Some countries rely on local sighting, others on different calculations, so a month may start a day earlier in one country than another.

4. Midnight or sunset

An evening event may traditionally fall on the next Hijri day while staying on the same Gregorian day.

For official transactions in Saudi Arabia, always rely on the date shown on the document or government platform itself. The converter is a tool for planning and quick checks, and it notes that religious months may start a day apart depending on sighting.

How conversion works

There’s no simple, accurate formula for converting by hand, because month lengths in Umm al-Qura are set astronomically, not by a fixed cycle. Popular approximations (such as multiplying the year by 0.97 and adding 622) only give the approximate year and can’t pin down a specific day. Accurate conversion needs Umm al-Qura tables or a system built on them.

An illustrative example: Tuesday 16 June 2026 corresponds to 1 Muharram 1448 AH in the Umm al-Qura calendar, and 1 Ramadan 1448 AH falls on 8 February 2027 in the same calendar (the actual start of Ramadan is set by sighting).

The converter works both ways, shows the weekday, warns you when the Hijri month you picked has only 29 days, and supports 1318–1500 AH (roughly 1900–2076 CE).

Dates in contracts and documents

Write both dates where possible: “Tuesday 1 Muharram 1448 AH, corresponding to 16 June 2026 CE”. Including the weekday prevents confusion if a day differs.
Specify the reference calendar in long contracts: are durations and payments calculated in Hijri or Gregorian? A Hijri year is about 11 days shorter, so a five-year contract differs by around 55 days depending on the calendar.
Rent and salaries: many transactions in Saudi Arabia now use the Gregorian calendar or combine both, so confirm which calendar each contract and system uses.
Numeric format: 1448-01-01 is clear, but always add “AH” so it isn’t read as a Gregorian date.

Showing Hijri dates on websites and apps

If you’re building a site or app for a Saudi audience, showing Hijri dates no longer requires heavy libraries. Modern browsers support it through Intl.DateTimeFormat with the islamic-umalqura calendar — the same approach our converter uses.

Specify the calendar explicitly (islamic-umalqura) rather than relying on the default, since some environments use another Hijri calendar.
Digits: decide whether to show Eastern Arabic numerals (١٤٤٨) or Western (1448), and stick to it site-wide.
Direction: mixed dates (numbers, month names, separators) can be reordered incorrectly inside Arabic text; isolate them directionally when needed.
Storage: store dates in the database in a standard Gregorian format and convert to Hijri only for display. This prevents calculation and sorting errors.
Test month boundaries: the last day of a Hijri month (29 or 30) and the start of a new year.

These details are part of the standards for company websites in Saudi Arabia, because they affect local users’ trust.

Common mistakes when handling both calendars

Adding 579 or 622 to the year directly: the gap between the two years isn’t fixed because the Hijri year is shorter; these shortcuts often give the wrong number.
Assuming a Hijri month always has 30 days: some months have 29, so the date “30” doesn’t exist in them. The converter warns you when you pick a day that doesn’t exist.
Counting durations in months without naming the calendar: “six months” from a Hijri date ends on a different day from “six months” from the equivalent Gregorian date.
Relying on your phone’s calendar without checking its type: some devices are set to a Hijri calendar other than Umm al-Qura.
Writing a Hijri date without “AH”, so systems and spreadsheets read it as an old Gregorian date.
Not reviewing appointments near the end of Ramadan and Dhu al-Hijjah, when Eid may shift with the sighting, moving holidays and related appointments.

Key takeaways

Umm al-Qura is Saudi Arabia’s official, pre-calculated Hijri calendar for civil purposes.
Religious months may start a day apart depending on moon sighting.
There’s no accurate manual formula; use a tool built on Umm al-Qura.
In contracts, write both dates with the weekday and name the reference calendar for durations.
In sites and apps, store Gregorian dates and convert to Hijri only for display.

Frequently asked questions

How old am I in Hijri years?

Convert your birth date to Hijri, then calculate the difference from today’s Hijri date. Because the Hijri year is shorter, your Hijri age is slightly higher than your Gregorian age — about one extra year for every 33.

Does conversion work offline?

Once the page has loaded, the calculation happens entirely in your browser, and no dates are sent to a server.

What do “AH” and “CE” mean?

“AH” (Anno Hegirae) means Hijri — counted from the Prophet’s migration — and “CE” means the Common (Gregorian) Era. Always write them after the year to avoid confusion.

The right date in a contract or appointment prevents needless disputes. Convert dates accurately with our free Hijri date converter — and if you’re building an Arabic website or app that needs proper support for both calendars and text direction, get in touch.