Hijri vs Gregorian Calendar: The Differences in Numbers

Hijri calendar · 7 min read · Last updated: 29 October 2026

If you live between two calendars, using the Gregorian for work and school and the Hijri for worship and festivals, it helps to know in numbers how they differ and why dates cannot be converted by a simple rule such as adding a fixed number of days.

A lunar calendar and a solar calendar

The Hijri calendar is lunar: it counts months by the Moon's cycles, and a month has 29 or 30 days. The Gregorian calendar is solar: it ties the year to the Earth's orbit around the Sun, so the seasons fall in the same months each year. One is tied to the night sky, the other to climate and seasons.

The numbers: how far apart are the two years?

The gap is about 10.9 days a year, so each Hijri year starts about eleven days earlier in the Gregorian calendar than the one before.

Why does Ramadan move through the seasons?

This table gives 1 Ramadan in five consecutive years by Umm al-Qura, computed with the site's engine:

Ramadan moves about 10 to 12 days earlier each year (1 March 2025, then 18 February 2026, then 8 February 2027), so it passes through every season. Thirty-three Hijri years are roughly 32 Gregorian years (33 × 354.37 = 11,694 days, about 32 years), so Ramadan returns to the same season after about 33 Hijri years. Fasting hours and heat change accordingly: long summer days mean longer fasts, short winter days shorter ones.

The first of Muharram over five years

The Hijri new year slips back ten or eleven days each Gregorian year and passes through all the Gregorian months in about thirty-three years.

The effect on age

Because the Hijri year is shorter, your Hijri age is larger than your Gregorian age; a hundred Gregorian years equal about 103 Hijri years. A worked example: from 15 March 2020 (20 Rajab 1441 AH) to 29 October 2026 (18 Jumada al-Ula 1448 AH) is 2,419 days. In Gregorian terms that is 6 years, 7 months and 14 days; in Hijri terms 6 years, 9 months and 28 days. Same period, different numbers. For your exact age use the age calculator.

Is there a conversion formula?

There is an approximate formula for the Gregorian year matching a Hijri year: Gregorian year ≈ Hijri year × 0.97023 + 621.57. For 1448 AH it gives about 2026.5, meaning 1448 starts around mid-2026 (it actually starts on 16 June 2026). But this estimates the year only and cannot give the day, which depends on the exact moment of the crescent. For the exact day use the Hijri to Gregorian converter or the Gregorian to Hijri converter.

Where the count begins

Hijri dating starts from the Prophet's ﷺ migration from Mecca to Medina in about 622 CE, adopted in the time of the caliph Umar ibn al-Khattab. According to the tabular calendar, the first day of year 1 (1 Muharram) falls in July 622 CE, not on the day of the migration itself. The popular account is that the companions chose the migration as the starting point, with Muharram as the first month; we mention it as widely reported history without settling its details.

The Gregorian calendar began with the Julian system and was reformed in the sixteenth century under Pope Gregory XIII; its leap-year rule is that years divisible by 4 are leap years, except century years not divisible by 400. That is why 2000 was a leap year and 1900 was not.

What this means in practice

• Fasting hours: Ramadan in summer means long, hot days; in winter, short ones. After about sixteen years it moves from one to the other.
• Yearly planning: do not set leave or travel by last year's Gregorian date; compute the new date each year.
• Contracts and subscriptions: a "year" in Hijri differs from a Gregorian "year" by about 11 days. Check which calendar the contract specifies.
• Ages: rules that require a given age in Hijri or Gregorian can give different results at the margin, so read the rule you are subject to.

Common questions

Do I just add ten days to find next year's date? For a rough idea, subtract about 10 to 12 days from the Gregorian date each year; but for the right day use the converter, because the gap may be 10, 11 or 12.

Is there a leap year in the Hijri calendar? In tabular calendars a day is added to Dhu al-Hijjah in some years to give 355 days. In Umm al-Qura there is no fixed rule; a year has 354 or 355 days depending on the real month lengths (in the site's range, 115 years of 354 days and 68 of 355).

Why do countries use both calendars? Civil life, work and education follow the seasons, while worship follows the Moon, which is why converting between them is a daily need.

In short

The Hijri year is about eleven days shorter, so events move through the seasons and Hijri ages are larger. Use the tools for the exact day rather than the rough rule. Remember that conversion is not always official: the result may differ by a day from your country's announcement (see Moon Sighting or Calculation).

Why there is no leap day every four years in the Hijri calendar

The Gregorian calendar adds a day to February every four years (with the century exception) to keep the seasons aligned with the Sun. The Hijri calendar has no such correction against the Sun, because it is not meant to follow the seasons; its months simply follow the Moon, and the only adjustment is that a month has 29 or 30 days. That is why a Hijri date cannot be fixed to a season, and why converting needs a table or algorithm rather than a rule such as "add 579 years".