This Islamic Hijri calendar converter lets you translate any Gregorian date into its Hijri (Islamic lunar calendar) equivalent, and convert Hijri dates back into the Gregorian calendar — using the traditional tabular arithmetic method followed by historians and calendar makers for over a millennium.
Pick a tab: "Gregorian → Hijri" if you have a modern calendar date, or "Hijri → Gregorian" if you have an Islamic date. Enter the date, press the convert button (or hit Enter), and the tool instantly returns the equivalent date on the other calendar, complete with the day of the week and full month name.
Muslims around the world use the Hijri calendar to mark religious observances — Ramadan fasting, Eid al-Fitr, Eid al-Adha, and the Hajj pilgrimage to Mecca all follow the lunar Islamic months rather than the Gregorian solar calendar. Historians, genealogists, and archivists also need this conversion constantly: Ottoman land records, Mughal court documents, medieval Arabic manuscripts, and mosque inscriptions are almost always dated in the Hijri era. A researcher reading a 14th-century waqf deed dated "12 Rajab 750 AH" needs to know that corresponds to September 1349 CE to place it correctly in world history. Genealogists tracing family records from the Middle East, South Asia, or North Africa run into Hijri dates on birth certificates and gravestones. Because the Islamic year is roughly 354 days — about 11 days shorter than the solar year — every Gregorian year the Hijri calendar drifts earlier, so a fixed conversion tool like this one saves hours of manual calculation.
This converter uses the tabular (arithmetic) Islamic calendar, the standard rule-based system used for civil and historical calculations (as opposed to the observational calendar based on physical moon-sighting, which can vary by a day depending on location and weather). Both calendars are first converted to a Julian Day Number (JDN) — a continuous day count used by astronomers and historians — then converted to the target calendar:
Gregorian → JDN:
JDN = ⌊1461×(Y+4800+a)/4⌋ + ⌊367×(M−2−12a)/12⌋ − ⌊3×⌊(Y+4900+a)/100⌋/4⌋ + D − 32075, where a = ⌊(M−14)/12⌋
JDN → Hijri:
Year = ⌊(30×(JDN−1948440)+10646)/10631⌋, using the epoch JDN 1,948,440 = 1 Muharram, AH 1 (16 July 622 CE). Each Hijri month alternates roughly 30/29 days across a 30-year cycle that keeps the calendar's average year at 354.367 days.
Because this is an arithmetic approximation, the result may differ by ±1–2 days from a locally observed Hijri calendar (such as Saudi Arabia's Umm al-Qura calendar), which depends on actual moon sighting.
Let's convert January 1, 2025 (Gregorian) to Hijri:
1. Convert the Gregorian date to a Julian Day Number using the formula above: JDN = 2,460,676.
2. Apply the JDN-to-Hijri formula with epoch 1,948,440: Year = ⌊(30×(2,460,676−1,948,440)+10646)/10631⌋ = 1446.
3. Work out the month and day within that Hijri year using the same 29.5-day month approximation.
4. Result: 1 January 2025 CE ≈ 1 Rajab 1446 AH (a Wednesday).
Try it yourself in the tool above — enter 2025-01-01 in the Gregorian tab and press Convert.
The Islamic calendar begins with the Hijra — the migration of the Prophet Muhammad from Mecca to Medina in 622 CE. Caliph Umar ibn al-Khattab formally established this event as Year 1 of the Islamic era around 638 CE, choosing a purely lunar calendar of twelve months (no leap months) to keep it independent of agricultural seasons, unlike the solar-based Julian and Gregorian systems. Each month traditionally began with the sighting of the new crescent moon, but by the medieval period scholars and astronomers developed the tabular arithmetic calendar used here — a fixed 30-year cycle with 11 leap years of 355 days and 19 common years of 354 days — so that scribes, tax collectors, and record keepers could compute dates without waiting for observation.
• Because the Hijri year is about 11 days shorter than the solar year, Ramadan shifts earlier every year and cycles through all four seasons roughly once every 33 solar years.
• The word "Hijra" literally means "migration" or "emigration," referring to the journey from Mecca to Medina, not the founding of Islam itself, which occurred about 12 years earlier.
• Some countries, notably Saudi Arabia, use the Umm al-Qura calendar (based on astronomical calculation, not the simple tabular method) for civil purposes, which can shift dates by a day compared to this converter.
It uses the standard tabular (arithmetic) Islamic calendar, accurate to within 1–2 days of observation-based calendars used in some countries. For legal or religious purposes, always confirm with an official moon-sighting authority.
The Gregorian calendar is solar with 365–366 days per year, while the Hijri calendar is purely lunar with 354–355 days per year and no leap months, causing it to drift about 11 days earlier each Gregorian year.
As of the Gregorian year 2025, the Hijri year is approximately 1446–1447 AH, depending on the exact Gregorian date, since the Hijri new year does not align with January 1st.
Because the Islamic calendar is lunar and about 11 days shorter than the solar year, each Islamic month — including Ramadan — starts roughly 11 days earlier on the Gregorian calendar than it did the previous year.
Yes — enter the day, month, and year exactly as written in the source, and the tool will return the corresponding Gregorian date using the standard tabular conversion formula used by historians.
"AH" stands for Anno Hegirae, Latin for "in the year of the Hijra," referring to the migration of the Prophet Muhammad from Mecca to Medina in 622 CE, which marks Year 1 of the Islamic calendar.
Calculator by HistoryCalc