Every year, hundreds of millions of Muslims around the world celebrate two different birthdays: their Gregorian birthday, which most people know, and their Hijri (Islamic) birthday, which follows the lunar calendar. Because the Islamic year is 11 to 12 days shorter than the solar year, your age in the Hijri system is always slightly higher than your age in the Gregorian system — and the two dates drift apart over time in a pattern that surprises many people.
If you want to see the difference between age systems side by side, try our Chinese age calculator for another example of how calendar systems change age, or use the lunar age calculator for a lunar-based perspective.
The Hijri Calendar: A Pure Lunar System
The Hijri calendar, also called the Islamic or lunar Hijri calendar, was established by Caliph Umar ibn al-Khattab in 638 CE (17 AH). Its epoch — the starting point — is the Hijra, the Prophet Muhammad’s migration from Mecca to Medina in 622 CE. The calendar is purely lunar: each month begins at the first sighting of the new crescent moon, and a year contains exactly 12 lunar months totaling 354 or 355 days.
Because the Hijri year is about 11 days shorter than the 365.25-day solar year, the calendar rotates through the seasons over a 33-year cycle. Ramadan, for example, moves about 11 days earlier in the Gregorian calendar each year and takes about 33 years to return to the same season.
The Math: Converting Between Gregorian and Hijri Age
The standard conversion formula between the two calendars is:
Gregorian year approximately equals Hijri year times 0.97 plus 622
To convert a Gregorian year to Hijri: Hijri year approximately equals (Gregorian year minus 622) times 1.03
The 0.97 and 1.03 factors account for the difference between the 354-day lunar year and the 365.25-day solar year. This is why a person born in 2000 in the Gregorian calendar was born in approximately 1420-1421 AH in the Hijri calendar — and why someone born on January 1, 2000 would be 26 years old in the Hijri system by 2026, while being 26 in the Gregorian system as well (the difference compounds only when your birthday falls on different dates in each system).
Why Your Hijri Age Is Often 1 Year Higher
Here is the counterintuitive part: because the Hijri year is shorter, you accumulate Hijri years faster. Over 33 Gregorian years, you gain approximately 34 Hijri years. In practice, this means:
- A 30-year-old in the Gregorian system is approximately 31 in the Hijri system
- A 50-year-old in the Gregorian system is approximately 52 in the Hijri system
- A 70-year-old in the Gregorian system is approximately 73 in the Hijri system
| Gregorian Age | Approximate Hijri Age | Difference |
|---|---|---|
| 10 | 10 | 0 |
| 20 | 21 | +1 |
| 33 | 34 | +1 |
| 40 | 41-42 | +1 to +2 |
| 50 | 52 | +2 |
| 66 | 68-69 | +2 to +3 |
| 70 | 73 | +3 |
Note that the difference is not a clean integer — it depends on exactly where each of your birthdays falls in each calendar. Someone whose Gregorian birthday and Hijri birthday both fall in the same week will show a smaller difference than someone whose birthdays land months apart.
Real Example: Ahmed’s Two Birthdays
Consider a concrete example. Ahmed was born on March 15, 1996 (Gregorian), which corresponds to 25 Shawwal 1416 in the Hijri calendar.
- March 15, 2026: Ahmed turns 30 in the Gregorian calendar
- May 7, 2026: Ahmed turns 31 in the Hijri calendar (25 Shawwal 1447)
For roughly two months out of every year, Ahmed is a different age in the two systems — 30 in one, 31 in the other. On official documents in countries that use the Hijri calendar (like Saudi Arabia), his legal age would be recorded as 31, which affects everything from legal majority to employment eligibility to retirement calculations.
Where the Hijri Calendar Is Used Today
The Hijri calendar is the official civil calendar in Saudi Arabia and is widely used alongside the Gregorian calendar in Muslim-majority countries for religious purposes. Several countries use it for specific administrative functions:
- Saudi Arabia: Official civil calendar; birth dates on official documents are often recorded in Hijri dates
- Morocco, Algeria, Tunisia: Used for religious holidays; Gregorian for civil administration
- Indonesia, Malaysia: Hijri dates used for Islamic holidays; Gregorian for legal purposes
- Iran and Afghanistan: Use the Solar Hijri calendar (a solar variant, not the lunar one), which tracks the Gregorian year length more closely
This dual-calendar system creates a real administrative challenge. A person’s official age can differ by a year depending on which calendar the issuing authority uses, which is why many Gulf countries now record both dates on identity documents.
Hijri vs. Chinese vs. Gregorian: Three Ways to Count Age
| System | Calendar Basis | Year Length | Age at Birth | Birthday Increment |
|---|---|---|---|---|
| Gregorian (Western) | Solar | 365/366 days | 0 | Each solar birthday |
| Hijri (Islamic) | Lunar | 354/355 days | 0 | Each lunar birthday (~11 days earlier each year) |
| Chinese (East Asian) | Lunisolar | 354-385 days (varies) | 1 (traditional) | Each Lunar New Year |
Unlike the Chinese system — where everyone gains a year simultaneously at Lunar New Year and babies are considered 1 year old at birth — the Hijri system increments age on each individual’s lunar birthday. This makes Hijri age closer to the Gregorian concept, just on a faster clock. The Islamic system also does not use the age 1 at birth convention, so a newborn is 0 in both Hijri and Gregorian systems, but their second Hijri birthday arrives about 11 days sooner than their second Gregorian birthday.
Practical Impacts of Hijri Age
The roughly 3% difference between Hijri and Gregorian age has real consequences:
- Legal majority: In Saudi Arabia, the age of majority is 18 in Hijri years which equals about 17.5 Gregorian years
- Marriage age: Some Islamic legal jurisdictions use Hijri age for minimum marriage age calculations
- Retirement: Civil service retirement in Saudi Arabia typically kicks in at 60 Hijri years (about 58.2 Gregorian years)
- Driving and ID: Driving licenses and national IDs issued in Hijri dates may show an age one year higher than the Gregorian equivalent
Frequently Asked Questions
How do I calculate my Hijri age?
Take the number of full lunar years that have passed since your birth date in the Hijri calendar. If you know your Gregorian birth date, you can convert it to Hijri, or you can estimate using the formula: Hijri age = (Gregorian age times 365.25) divided by 354.37. For most people, this results in a Hijri age 1-3 years higher than their Gregorian age.
Is the Hijri calendar the same as the Chinese lunar calendar?
No. The Hijri calendar is a pure lunar calendar with no intercalation (leap months). The Chinese calendar is lunisolar — it adds a 13th month roughly every 3 years to keep the lunar months aligned with the solar seasons. This is why Chinese New Year always falls between January 21 and February 20, while Islamic months drift through all seasons.
Which age does Saudi Arabia use for official purposes?
Saudi Arabia officially uses the Hijri calendar for civil administration. Birth dates, ID documents, employment records, and age-based legal thresholds (majority, driving age, retirement) are typically calculated in Hijri years. Many government digital services now show both Hijri and Gregorian dates to reduce confusion.
Does the Solar Hijri calendar (Iran) give the same age as Gregorian?
Almost. The Solar Hijri calendar used in Iran and Afghanistan is a solar calendar with 365 days (366 in leap years), so ages calculated in it are nearly identical to Gregorian ages — the difference is at most a few days, not a full year. The famous Iranian age difference applies only to the lunar Hijri calendar used in Saudi Arabia and other Gulf states.
Age systems around the world vary more than most people expect. To explore other examples, try the Korean age calculator or the Japanese age calculator — both use completely different conventions for counting age.
