Islamic Date Calculator
Calculate days between two Hijri dates or convert Hijri date ranges to Gregorian. Enter values for instant results with step-by-step formulas.
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer
Islamic Date Calculator
Calculator
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Formula: JD = floor((11Y+3)/30) + 354Y + 30M - floor((M-1)/2) + D + 1948440 - 385
Worked example — 162 days | 23 weeks 1 day | Approx 5.5 months
Formula
JD = floor((11Y+3)/30) + 354Y + 30M - floor((M-1)/2) + D + 1948440 - 385
This formula converts a Hijri date to a Julian Day Number (JD) using the tabular Islamic calendar. Y is the Hijri year, M is the month, and D is the day. The Julian Day Number can then be converted to Gregorian or used to compute date differences.
Worked Examples
Example 1: Days Between Two Hijri Dates
Problem:Calculate the days between 1 Muharram 1446 AH and 15 Jumada al-Thani 1446 AH.
Solution:1 Muharram 1446 = JD 2460493 (approx July 7, 2024) 15 Jumada al-Thani 1446 = JD 2460657 (approx Dec 18, 2024) Months: Muharram(30) + Safar(29) + Rabi I(30) + Rabi II(29) + Jumada I(30) + 14 days of Jumada II Days = 30 + 29 + 30 + 29 + 30 + 14 = 162 days Weeks = 23 weeks and 1 day
Result:162 days | 23 weeks 1 day | Approx 5.5 months
Example 2: Hijri to Gregorian Conversion
Problem:Convert 1 Ramadan 1447 AH to the Gregorian calendar.
Solution:Using the tabular Hijri-to-JD conversion: JD = floor((11 x 1447 + 3) / 30) + 354 x 1447 + 30 x 9 - floor(8/2) + 1 + 1948440 - 385 Convert JD to Gregorian date using standard algorithm. 1 Ramadan 1447 AH falls in February 2026.
Result:1 Ramadan 1447 AH = approximately February 2026 CE
Frequently Asked Questions
How does the Islamic (Hijri) calendar work?
The Islamic calendar, also known as the Hijri calendar, is a purely lunar calendar consisting of 12 months that alternate between 29 and 30 days. A standard Hijri year contains 354 days, which is about 11 days shorter than the Gregorian solar year. This means Islamic dates shift earlier relative to the Gregorian calendar by approximately 11 days each year. The calendar begins from the year of the Hijra, Prophet Muhammad's migration from Makkah to Madinah in 622 CE. Odd-numbered months have 30 days and even-numbered months have 29 days, except in leap years when the 12th month Dhul Hijjah has 30 days instead of 29.
What are leap years in the Hijri calendar?
The Hijri calendar uses a 30-year cycle containing 11 leap years. In a leap year, the last month Dhul Hijjah has 30 days instead of the usual 29, making the year 355 days instead of 354. The leap years occur at positions 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29 within each 30-year cycle. To determine if a Hijri year is a leap year, divide the year by 30 and check if the remainder matches one of these positions. For example, 1446 AH divided by 30 gives a remainder of 6, which is not in the list, so 1446 AH is a common year with 354 days.
How accurate is the tabular Islamic calendar for conversions?
The tabular Islamic calendar used in Islamic Date Calculator is an arithmetic approximation of the observational Islamic calendar. It can differ from the actual observed calendar by one to two days because the observational calendar depends on physical sighting of the crescent moon, which varies by geographic location and weather conditions. For historical dates and general planning, the tabular calendar is sufficiently accurate and widely used in astronomy and computing. Saudi Arabia and many Muslim-majority countries use the Umm al-Qura calendar for civil purposes, which may differ slightly from the tabular system used here.
Why do Islamic holidays shift dates every year in the Gregorian calendar?
Islamic holidays appear to move earlier by about 10 to 12 days each Gregorian year because the Hijri calendar year is approximately 354 days compared to the Gregorian year of 365 or 366 days. This difference of roughly 11 days means that Ramadan, Eid al-Fitr, Eid al-Adha, and other Islamic observances cycle through all seasons over a period of about 33 Gregorian years. This is by design in the Islamic tradition, as the lunar calendar ensures that religious duties like fasting during Ramadan are experienced in every season, making the obligation equitable across different climates and day lengths.
What are the twelve months of the Islamic calendar?
The twelve months of the Islamic calendar are Muharram, Safar, Rabi al-Awwal, Rabi al-Thani, Jumada al-Ula, Jumada al-Thani, Rajab, Shaban, Ramadan, Shawwal, Dhul Qadah, and Dhul Hijjah. Four of these are considered sacred months (Muharram, Rajab, Dhul Qadah, and Dhul Hijjah) during which warfare was traditionally prohibited. Ramadan is the month of fasting. Shawwal begins with Eid al-Fitr. Dhul Hijjah contains the Hajj pilgrimage period and concludes with Eid al-Adha. Each month begins with the sighting of the new crescent moon, though the tabular calendar uses mathematical rules for calculation.
What is ISO 8601 and why should I use it for dates?
ISO 8601 formats dates as YYYY-MM-DD (e.g., 2025-03-15), eliminating ambiguity between US (MM/DD/YYYY) and European (DD/MM/YYYY) formats. It sorts chronologically as text, is internationally recognized, and is the standard for data exchange and APIs.
Should I count dates inclusively or exclusively?
It depends on context. Age is counted exclusively (born Jan 1, you turn 1 on the next Jan 1). Rental periods are usually inclusive of the start date and exclusive of the end date. Legal deadlines vary by jurisdiction. Always clarify which method applies.
How do I calculate the number of working days between two dates?
Count total calendar days, subtract weekends (roughly 2/7 of total days), then subtract any public holidays in the range. For accuracy, iterate through each day and check. Most spreadsheets have NETWORKDAYS functions that handle this automatically.
Does a leap year affect date difference calculations?
Leap years add February 29, extending the year to 366 days and affecting any date range spanning that date. January 1 to December 31 is 365 days in a regular year but 366 in a leap year. Applications must define whether "one year from February 28" maps to February 28 or 29 in a leap year. Financial instruments use specific day-count conventions — Actual/360, Actual/365, or Actual/Actual — to handle these edge cases consistently.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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