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 fall on our regular calendar. I said “around April.” I was three weeks off.

The Hijri calendar helps track time in many Muslim communities. It does not line up exactly with the Gregorian calendar we use for flights and meetings. Once you know how each system works and where they differ, converting dates takes only a few seconds.

This article explains how to convert dates between Gregorian and Hijri. It shows why conversions can differ by a day. It also explains which conversion method is most reliable. 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 began on July 16, 622 CE. That day marks the Hijra when Prophet Muhammad ﷺ moved from Makkah to Madinah. Each month follows the moon’s cycle. People start a new month when they see the new crescent moon (Hilal).

Key facts to know:

• Year length: 354 days. That equals 12 lunar months at about 29.5 days each.
• Drift from Gregorian: The Hijri year is about 11 days shorter than the Gregorian year. As a result, Hijri dates move backward by about 11 days on the Gregorian calendar each year.
• Leap years: There are 11 leap years in a 30-year cycle. They are years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29. In a leap year, the last month gains an extra day.
• Month lengths: In a fixed Hijri system, months alternate between 30 and 29 days. In observational systems, people decide a month’s length by seeing the moon.

The 12 Months of the Hijri Calendar

Two Kinds of Hijri Calendars Used Today

This difference often causes people to say, “My converter doesn’t agree with yours!” There are two main types in use.

1. The Fixed (Astronomical) Hijri Calendar

This calendar uses set rules to fix month dates in advance. Saudi Arabia’s Umm al-Qura calendar follows this method. It also adjusts based on the expected new moon in Makkah. You find this type in:

• Most printed calendars worldwide
• 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 starts only when a trusted person actually sees the new crescent moon. Groups that use this include:

• Many Muslim communities that decide Ramadan’s start and end by sighting
• Hajj timing in Saudi Arabia (the moon sighting is reported to Riyadh)
• Local Hilal Committees in the UK, US, Canada, Australia, and South Africa

The observational system can begin a month one day later than the fixed system. This happens if clouds or bad weather hide the crescent on the expected night. That difference explains why Eid al-Fitr may be observed on different days in nearby countries. Both approaches follow their own valid rules.

Converting Gregorian to Hijri — The Math Behind It

Most modern converters use a math method from Jean Meeus’s book Astronomical Algorithms. They then update it with the Umm al-Qura tables for years 1300 AH to 1500 AH. Below is a simpler view of the steps.

1. Convert the Gregorian date to a Julian Day Number (JDN).
2. Calculate the Hijri year (H) from the JDN using this formula: H = floor((JDN − 1948440 + 10632) / 10631) × 30 + floor(((JDN − 1948440 + 10632) mod 10631 + 354.367) / 354.367).
3. Compute the JDN for 1 Muharram of that Hijri year.
4. Subtract to get the day number within the Hijri year (1 to 354 or 355).
5. Walk through the months (30, 29, 30, 29 days, adding the leap day if needed) until you find the correct Hijri month and day.

This approach is usually accurate within one day for years between 1356 AH (1937 CE) and 1500 AH (2076 CE). For dates much older or beyond that range, it can be slightly less exact. Our Hijri date converter does the math for 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 the moon sighting.

Important Global Dates

How to Use a Hijri Converter for Everyday Planning

I find these converters helpful for many tasks.

1. Plan Around Ramadan

Knowing roughly when Ramadan will start months ahead helps plan travel, work, and family events. I use the converter to view the next 3 to 5 Ramadans.

2. Mark Islamic Anniversaries

Many Muslim families track weddings, deaths, and naming ceremonies by Hijri dates. I convert those dates to Gregorian once a year. That helps 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 began on 1 Muharram 1444 AH, the next anniversary is 1 Muharram 1445 AH. That will fall on a different Gregorian date each year. You can use the Hijri date converter with our Zakat calculator to track this automatically.

4. Confirm Hajj Dates

Hajj rituals occur on specific Hijri dates (8–13 Dhul-Hijjah). Flights and visas use Gregorian dates. Converting is the only way to ensure everything lines up for the same year.

Common Mistakes When Converting Dates

Watch out for these common errors.

• Forgetting that days start at sunset in Islam. For example, 12 Ramadan technically begins at sunset on the day before. For most tasks, like booking flights, using the Gregorian “civil day” is fine. For religious acts, like starting a fast or timing prayers, sunset matters.
• Using a calendar that mixes rules. Some apps use fixed tables but adjust Ramadan to match local moon-sighting committees. Read the app’s notes to understand its rules.
• Thinking Hijri dates match the seasons. The Hijri calendar moves by about 11 days each year. Over 33 years, Ramadan cycles through every season. Your Hijri birthday will fall in different seasons over decades.
• Mixing up Hijri AH with AD/CE. The current year is 1447 AH (it began in mid-2025 CE). AH years count from the Hijra and are not the same as AD/CE.

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 sighting. That is why neighboring countries may celebrate Eid one day apart.

Is the Hijri calendar used for things other than religion?

Yes. Saudi Arabia uses the Umm al-Qura calendar for official purposes. That includes government work, salaries, school years, and ID cards. Iran uses a different solar Hijri calendar (Hijri Shamsi) tied to the spring equinox. That solar calendar is different from the lunar Hijri calendar discussed 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 reliable up to 1500 AH (about 2076 CE). After that, the method becomes more of an estimate. For rigorous research, consult 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 used by much of the Islamic world. Hijri Shamsi is a solar calendar used officially in Iran and Afghanistan. The solar calendar ties months to the sun’s year and marks New Year 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 make one Hijri month at a time using our Hijri date converter. Then combine them into a full sheet. Many printed Hijri calendars, like those from the Saudi Press Agency or local Islamic Centers, already show 12 months of Hijri and Gregorian dates side-by-side for printing.

Wrapping Up

The Hijri calendar is not harder than the Gregorian calendar. It is just built differently. Once you know it has 354 days, a 30-year leap cycle, and the difference between fixed and observational methods, you will not be surprised when Ramadan falls on new Gregorian dates each year. The CalcaTools Hijri date converter works both ways, supports both methods, and covers any year you need. Next time someone asks “when is 13 Dhul-Hijjah?” you can get the answer in five seconds without guessing. Use it with our Zakat calculator to plan your full Islamic financial year and cover most calendar tasks.

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.

In plain language

Hijri to Gregorian Conversion: How the Islamic Calendar W… can be understood by starting with the definition on this page. Keep every input in the same unit. Check the result against a reasonable estimate. Short sentences and one-step checks make the method easier to follow and reduce avoidable mistakes.