Hijri to Gregorian Conversion: How the Islamic Calendar W…

The night before my flight to Madinah for Umrah a few years ago, my aunt called. She asked when “13 Dhul-Hijjah” would be on our normal calendar. I quickly said “around April.” I was three weeks off!

The Hijri calendar is a really useful way to keep track of time. But it doesn’t line up perfectly with the Gregorian calendar we use for flights and meetings. Once you learn how they work together, and where they differ, converting dates takes only a few seconds.

This article will show you how to change dates from Gregorian to Hijri and back. You’ll also learn why the two calendars can sometimes be a day apart. Plus, I’ll tell you which conversion method is the most trustworthy. Our free Hijri date converter uses the Umm al-Qura method. This is the most accepted way to convert dates in 2026.

What is the Hijri Calendar?

The Hijri calendar is a moon-based calendar. It started on July 16, 622 CE. This was the day Prophet Muhammad ﷺ moved (Hijra) from Makkah to Madinah. Each month follows the moon’s cycle. A new month begins when people see the new crescent moon (Hilal).

Here are some key things to know:

• Year length: It has 354 days. This is 12 lunar months, each about 29.5 days long.
• Drift from Gregorian: It’s 11 days shorter than the Gregorian year. So, Hijri dates “move backward” by 11 days each year on the Gregorian calendar.
• Leap years: There are 11 leap years in every 30-year cycle. These are years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29. In a leap year, the last month gets an extra day.
• Month lengths: In a fixed Hijri system, months switch between 30 and 29 days. But in systems where people actually look for the moon, the real sighting decides how long the next month will be.

The 12 Months of the Hijri Calendar

Two Kinds of Hijri Calendars Used Today

This is often why people say, “My converter doesn’t agree with yours!” There are two main types:

1. The Fixed (Astronomical) Hijri Calendar

With this calendar, month dates are figured out ahead of time using a set rule. Saudi Arabia’s Umm al-Qura calendar uses this method. It also adjusts based on when the new moon is expected in Makkah. This type is used by:

• Most printed calendars around the world
• Saudi Arabia’s official calendar (Umm al-Qura)
• Most online Hijri date converters and apps
• The Hijri options in Microsoft Office, Apple Calendar, and Google Calendar

2. The Observational Hijri Calendar

In this system, a new month officially starts only when a trusted person actually sees the new crescent moon. This method is used for:

• Deciding when Ramadan starts and ends for many Muslim groups
• Timing the Hajj in Saudi Arabia (the moon sighting is reported to Riyadh)
• Local Hilal Committees in places like the UK, US, Canada, Australia, and South Africa

The observational system can start a month one day later than the fixed system. This happens if bad weather or clouds hide the crescent moon on the night it’s expected. This is why Eid al-Fitr might be celebrated on different days in nearby countries. Both communities are following their own rules correctly.

Converting Gregorian to Hijri — The Math Behind It

Most modern converters use a version of a math method from a book called Astronomical Algorithms by Jean Meeus. It’s then updated with the Umm al-Qura tables for years 1300 AH to 1500 AH. Here’s a simpler look at how it works:

1. First, the Gregorian date is changed into a Julian Day Number (JDN).
2. Next, the Hijri year (H) is figured out from the JDN using a complex formula: H = floor((JDN − 1948440 + 10632) / 10631) × 30 + floor(((JDN − 1948440 + 10632) mod 10631 + 354.367) / 354.367).
3. From that Hijri year, the JDN for the 1st of Muharram of that year is calculated.
4. Then, they subtract to find the day number within that Hijri year (from 1 to 354 or 355).
5. Finally, they go through the months (30, 29, 30, 29 days, with the leap day if needed) until they find the right Hijri month and day.

This method is usually correct within one day for any year between 1356 AH (1937 CE) and 1500 AH (2076 CE). For dates much older or newer, it might be a little less exact. Our Hijri date converter does all this math for you. You just pick the date!

Examples of Date Conversion

Gregorian → Hijri

September 11, 2026 Gregorian becomes 28 Rabi al-Awwal 1448 AH (using the fixed Umm al-Qura method).

Hijri → Gregorian

1 Ramadan 1448 AH is about February 11, 2027 Gregorian (this can change based on when the moon is sighted).

Important Global Dates

How to Use a Hijri Converter for Everyday Planning

I find these converters super helpful for many things:

1. Plan Around Ramadan

Knowing roughly when Ramadan will start months ahead is a big deal. It helps me plan travel, work, and family events. I use the converter to see the next 3 to 5 Ramadans.

2. Mark Islamic Anniversaries

Many Muslim families remember important dates, like weddings, deaths, or naming ceremonies, by their Hijri date. I convert these to Gregorian once a year. This helps me line them up with school schedules and other plans.

3. Figure Out Zakat Anniversaries

Your Zakat year (Hawl) follows the lunar calendar. If your Hawl started on 1 Muharram 1444 AH, the next anniversary is 1 Muharram 1445 AH. This will be a different Gregorian date each year. You can use the Hijri date converter with our Zakat calculator to keep track automatically.

4. Confirm Hajj Dates

The Hajj rituals happen on specific Hijri dates (8–13 Dhul-Hijjah). But flights and visas are booked using Gregorian dates. Converting is the only way to make sure everything lines up for the same year.

Common Mistakes When Converting Dates

Watch out for these easy-to-make errors:

• Forgetting that days start at sunset in Islam. For example, 12 Ramadan technically begins at sunset on 11 Ramadan. For most normal things, like booking flights, using the Gregorian “civil day” is fine. But for religious practices, like when to start fasting or pray, sunset is very important.
• Using a calendar that mixes different rules. Some apps might use fixed tables but then change Ramadan dates to match a local moon sighting committee. Always read the app’s info to understand its rules.
• Thinking Hijri dates match the seasons. The Hijri calendar shifts by about 11 days each year. This means Ramadan moves through every season over a 33-year period. Your Hijri birthday will fall in a different season every couple of decades!
• Mixing up Hijri AH (After Hijra) with AD/CE. The current year is 1447 AH (it started in mid-2025 CE). You wouldn’t say “in the year 1447.” AH years are separate and count from the Hijra.

Frequently Asked Questions

Why do Muslim countries sometimes celebrate Eid on different days?

Eid depends on seeing the new crescent moon. If people in Saudi Arabia see the moon on the 29th of Ramadan, Eid is the next day. If clouds block the view that night, the month gets a 30th day, and Eid is one day later. Different countries use different groups to confirm the moon sighting. This is why neighboring countries might celebrate Eid exactly one day apart.

Is the Hijri calendar used for things other than religion?

Yes, it is. Saudi Arabia uses the Umm al-Qura calendar as its main official calendar. This includes things like government work, paying salaries, school years, and ID cards. Iran uses a different solar Hijri calendar (Hijri Shamsi) that follows the spring equinox. This is completely different from the lunar Hijri calendar we’re talking about here.

How can I find Islamic dates more than 50 years in the future?

Most online Hijri converters use the Umm al-Qura fixed method. This method is usually good up to 1500 AH (around 2076 CE). After that, the method can guess, but it’s less exact. For serious research, you can look at predictions from groups like the Saudi Astronomical Society.

What’s the difference between Hijri Shamsi and Hijri Qamari?

Hijri Qamari is the lunar Hijri calendar. Most of the Islamic world uses this one. Hijri Shamsi is a solar calendar. It’s used officially in Iran and Afghanistan. Its months are tied to the sun’s year, and New Year is on Nawruz (March 20–21). The Hijri date converter on this site focuses on the lunar Qamari calendar.

Can I print a full Gregorian-Hijri calendar for the year?

Yes, you can. You can make one Hijri month at a time using our Hijri date converter. Then you can put them together to make a full sheet. Many printed Hijri calendars, like those from the Saudi Press Agency or local Islamic Centers, already have 12 months of Hijri and Gregorian dates side-by-side, ready for printing.

Wrapping Up

The Hijri calendar isn’t “harder” than the Gregorian one – it’s just built differently. Once you know it has 354 days, a 30-year leap cycle, and how fixed and observational methods differ, you won’t be surprised when Ramadan starts on a new date each year. The CalcaTools Hijri date converter works both ways, for both methods, and for any year you need. So, the next time someone asks “when is 13 Dhul-Hijjah?” you’ll have the answer in five seconds, without guessing. Use it with our Zakat calculator to plan your full Islamic financial year. This way, most of your calendar tasks are covered.

Related Calculators and Guides

Check out more Hijri and Islamic date tools:

• Hijri Date Converter — change any Gregorian date to Hijri and back.
• Islamic Calendar — see the current Hijri month and important dates.
• Hijri Age Calculator — find out how old you are in the Islamic calendar.
• How to Calculate Zakat in 2026 — learn about zakat on the lunar year.
• What Is Nisab? — understand the gold and silver amount for zakat.