How to Calculate Islamic Date

Years in the Muslim Hijri calendar began with the Hijrah, Mohammad's journey from Mecca to Medina. He made the journey in the year 622 A.D. of the Gregorian calendar, so years in the Hijri differ from those in the Gregorian calendar. In addition, the Hijri uses 12 lunar months of 29 or 30 days each, so a Hijri year is about 11 days shorter than a Gregorian year. There is no straightforward conversion between the two systems, but you can closely approximate the Islamic date using a formula.

Things You'll Need

• Calculator

Instructions

1. Add together the number of days in each month preceding your date plus the month. To convert May 12, 2007, for example, add 31 days for January, 28 days for February, 31 days for March, 30 days for April and the 12 days in May to get 132 days.

2. Divide the result by 365 to convert from days to years. For example, 132 divided by 365 equals 0.361 years.

3. Add the fractional year to the year of the date, to express the date as a decimal year. For May 12, 2007, add 0.361 to 2007 to get 2007.361 years.

4. Subtract 621.54 from the decimal date. For example, 2007.361 minus 621.54 equals 1385.821.

5. Divide the result by 0.970255 to find the Islamic date expressed as a decimal year. For example, 1385.821 divided by 0.970255 equals 1428.35 years on the Hijri calendar.

6. Multiply the decimal portion of the Hijri date by 354 to get the day of the year. Multiply 0.35 by 354 to get the 124th day of the year, for example.

7. Subtract 30 and 29 alternately from the day of the year, until you reach a number lower than 29. For the 124th day, for example, subtract 29 and 30 two times each to get six. This means that four full months plus six days have passed in the year, so the date is the sixth day of the fifth month.

8. Write the date using the day of the month, the name of the Islamic month, the Islamic year and the abbreviation "A.H." For example, May 12, 2007 A.D. converts to 6 Jumada-al-Awwal 1428 A.H.

Tips & Warnings

• Do not round off the 0.970225 in the calculation, as using a less precise number will cause errors.

• Because of leap years in both the Hijri and Gregorian calendars, this calculation may be off by one day.

References

• The Ohio State University; An Introduction to the Islamic (Hijri) Calendar; Waleed Muhanna; December 1992
• "Israel Handbook: With the Palestinian Authority Areas"; Dave Winter; 1999

Resources

• Zurich University; Conversion of Islamic and Christian Dates; J. Thomann; May 2006