How to Convert Gregorian to Hijri Date: Complete Guide

Why Convert Between Gregorian and Hijri Dates?

For Muslims worldwide, knowing how to convert between the Gregorian (solar) calendar and the Islamic Hijri (lunar) calendar is an essential practical skill. The Hijri calendar governs Islamic religious life — it determines when Ramadan begins, when Eid falls, when Hajj takes place, and when other Islamic observances occur. Yet in most of the world, daily life runs on the Gregorian calendar.

Date conversion is needed for:

• Determining the Gregorian date of upcoming Islamic holidays (Ramadan, Eid, Hajj)
• Converting important personal dates (birth dates, marriage dates) to Hijri for Islamic purposes
• Paying Zakat (calculated based on the lunar Hijri year)
• Determining Hawl (one full lunar year for Zakat eligibility)
• Planning for Islamic events that shift each year
• Historical research involving both Islamic and Western history

Hijri Guide provides a free, accurate online converter for both Gregorian to Hijri and Hijri to Gregorian conversions. But understanding the underlying system makes you a more informed user of any conversion tool.

Understanding the Two Calendars

The Gregorian Calendar (Solar)

The Gregorian calendar is the internationally accepted civil calendar used in most of the world. It is a solar calendar — based on the Earth's orbit around the sun. A Gregorian year consists of 365 days (or 366 in a leap year), with months of 28-31 days that do not correspond to lunar cycles.

The Islamic Hijri Calendar (Lunar)

The Hijri calendar is a purely lunar calendar — each month begins with the sighting of the new crescent moon. A Hijri year consists of 12 lunar months, each lasting 29 or 30 days, for a total of 354 or 355 days per year.

The key difference: the Hijri year is approximately 10-11 days shorter than the Gregorian year. This means:

• Islamic months cycle through all Gregorian months over a period of approximately 33 years
• Ramadan, Eid, and other Islamic dates shift earlier each Gregorian year by about 10-11 days
• Islamic events fall in different seasons depending on the year (Ramadan has been in summer, winter, spring, and autumn)

The Starting Point: 1 Muharram 1 AH

The Hijri calendar begins from the year of the Hijra — the Prophet Muhammad's migration from Mecca to Medina in 622 CE. The first day of the Hijri calendar (1 Muharram 1 AH) corresponds to approximately July 16, 622 CE (Julian calendar).

The abbreviation "AH" stands for Anno Hegirae — Latin for "in the year of the Hijra," equivalent to the Arabic Hijri. This is analogous to "CE" (Common Era) or "AD" (Anno Domini) used with the Gregorian calendar.

The Calculation Method: Julian Day Numbers

The most mathematically precise method for converting between the Gregorian and Hijri calendars involves using Julian Day Numbers (JDN) — a continuous count of days from a fixed starting point in astronomy.

Step 1: Convert Gregorian Date to Julian Day Number

For a Gregorian date (year Y, month M, day D):

JDN = 367 × Y
     − INT(7 × (Y + INT((M + 9) / 12)) / 4)
     − INT(3 × (INT((Y + (M − 9) / 7) / 100) + 1) / 4)
     + INT(275 × M / 9)
     + D + 1721028.5

Step 2: Convert Julian Day Number to Hijri Date

Once you have the JDN, you can convert it to a Hijri date using the following approach:

N = JDN − 1948438.5 + 0.5 (roughly)
Q = INT(N / 10631)  ← number of Hijri 30-year cycles
R = N mod 10631
Z = 11 (if R > certain threshold) or lower
... (complex calculation continues)

The full algorithm is quite involved, which is why most people — and tools like Hijri Guide — use pre-programmed libraries like Moment-Hijri or the Al-Adhan API that handle these calculations accurately.

A Simple Approximation Method

For rough conversion without a calculator, you can use this approximation:

Gregorian to Hijri (approximate)

Hijri Year ≈ (Gregorian Year − 622) × (33/32)

For example:
2025 CE: (2025 − 622) × 33/32 = 1403 × 1.03125 ≈ 1447 AH ✓

Hijri to Gregorian (approximate)

Gregorian Year ≈ (Hijri Year × 32/33) + 622

For example:
1447 AH: (1447 × 32/33) + 622 ≈ 1403 + 622 ≈ 2025 CE ✓

Important: These approximations give the right year most of the time, but can be off by a year near the boundaries. For accurate date-specific conversions, always use an online conversion tool like Hijri Guide.

Worked Examples of Date Conversion

Example 1: Gregorian to Hijri

Convert: March 1, 2025 (Gregorian)

Using accurate astronomical calculation (as done by Hijri Guide):

• March 1, 2025 = 1 Ramadan 1446 AH
• This is approximately the start of Ramadan 2025

Example 2: Hijri to Gregorian

Convert: 1 Ramadan 1446 AH

• 1 Ramadan 1446 AH = approximately March 1-2, 2025 CE
• (Exact date may vary by 1 day based on moon sighting)

Example 3: Converting a Birthday

Convert: Born January 15, 1990 (Gregorian)

• January 15, 1990 = 18 Jumada al-Thani 1410 AH
• This person was born in the 6th month of Hijri year 1410
• Their next Hijri birthday in 1446 AH would be around December 19, 2024 CE

Moon Sighting vs. Calculation: Why Dates Sometimes Differ

One important reason why Hijri dates can differ by 1-2 days between countries and communities is the difference between calculated dates and actual moon sighting:

• Astronomical calculation: Precisely predicts when the new moon will be born and when it will first be visible. This allows dates to be published months in advance. Hijri Guide uses this method.
• Physical moon sighting: The actual crescent must be observed by witnesses on Earth. Clouds, atmospheric conditions, geographic location, and the angle of the moon can cause the sighting to be one day later than astronomically calculated, or different in different countries.

This is why Ramadan might start one day earlier in some countries than others, and why global Islamic dates often show a 1-day variance. Hijri Guide clearly indicates when dates are estimates and recommends verifying critical dates (like Ramadan start) with local Islamic authorities.

Using the Hijri Guide Date Converter

For the most accurate date conversions, use our free online tools:

• Gregorian to Hijri Converter: Enter any date in the Gregorian calendar and instantly see the equivalent Hijri date
• Hijri to Gregorian Converter: Enter any Hijri date and find the Gregorian equivalent
• Today's Hijri Date: See the current Hijri date with real-time accuracy

Our converters use the Moment-Hijri library combined with the Al-Adhan API for two-layer accuracy, with automatic fallback to ensure results are always available even when external services are down.

Common Questions About Date Conversion

How do I find the Hijri date of my birthday?

Enter your Gregorian birth date (DD/MM/YYYY) into the Gregorian to Hijri converter. The tool will display the equivalent Hijri date. Note that your Hijri birthday will fall on a different Gregorian date each year (shifting earlier by about 10-11 days annually).

Why does Ramadan fall on different dates each year?

Ramadan always falls in the 9th month of the Hijri calendar (1 Ramadan). But because the Hijri year is about 10-11 days shorter than the Gregorian year, this same Hijri month falls progressively earlier each Gregorian year, cycling through all Gregorian months over 33 years.

Is there an exact conversion formula?

There is a precise mathematical method (using Julian Day Numbers), but due to the variation between calculated moon visibility and actual moon sighting, there will always be a potential 1-day variance for any date that depends on physical moon sighting (like the start of Ramadan).

Conclusion

Converting between Gregorian and Hijri dates is an essential skill for Muslims who want to plan for Islamic holidays, calculate Zakat, and stay connected to the Islamic calendar. While the underlying mathematics is complex, tools like Hijri Guide make accurate conversion instant and accessible.

Understanding why the two calendars differ — and why dates shift by about 11 days each year — helps you confidently plan for Ramadan, Eid, Hajj, and other significant Islamic dates well in advance.