Q: We represent a corporation that offers installment sales. Mostly, our sales are divided on monthly installments for three years. It is subject to a certain amount of interest agreed upon at the time of endorsing the contract. The monthly installments the corporation recovers are reinvested in buying new commodities and offering them, again, in installment sales.We kindly request that you inform us of the method by which the Zakah (obligatory charity) is calculated in this activity. As-salamu `alaykum warahmatullah wabarakatuh (May Allah's Peace, Mercy, and Blessings be upon you!) A: Zakah is due upon a certain amount of money when the Hawl (one lunar year calculated from the time a property reaches the minimum amount upon which Zakah is due) passes with that amount being in the possession of its owner. The same applies on money that is lend to or borrowed by able non-procrastinating people, whether this debt is going to be paid as one payment or in installments. Zakah is also due upon any sale commodities if a Hawl passes and the value they were sold for is still in the possession of the owner. (Part No. 8; Page No. 127