In our country the approved calendar is the Gregorian one. The annual inventory of merchants is made at the end of every Gregorian year. Is this correct or should it be according to the Hijri calendar? If it should be according to the Hijri calendar, what is the solution concerning the previous years?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

What is considered with regards to the time of paying Zakah is the Hijri calendar. Allaah The Almighty Says (what means): {They ask you, [O Muhammad], about the new moons. Say, "They are measurements of time for the people and for Hajj."} [Quran 2:189]

Shaykh Al-Islam Ibn Taymiyyah said: “Allaah The Almighty Considered the lunar months timings for people in the confirmed rulings of Sharee‘ah as a starting point and a reason. This includes fasting, Hajj and Zakah.”

Adopting the Gregorian calendar for Zakah is invalid and it leads to delaying it and this is impermissible. However, if there is considerable difficulty to calculate it according to the Hijri calendar, it is permissible to calculate it with the Gregorian calendar as it is permissible to delay Zakah in case of need taking into account two issues:

1. Zakah is due from the owner of the wealth upon the completion of a lunar year which is about eleven days less than a Gregorian year.

2. It is obligatory to calculate the difference that results from the mentioned delay which is the Zakah of one lunar year upon the end of every thirty-three solar years. This answers the question about the ruling on the previous years.

Allaah Knows best.