I sell cars by installment, so how do I pay Zakat on this money?

Zakat is obligatory on cars designated for trade if they reach the nisab (threshold) and a full year (hawl) has passed on them. One-quarter of one-tenth (2.5%) of their market value at the completion of the year is to be given out. Installments owed by customers are to be added to one's wealth and zakat paid on them, unless the debtor is procrastinating or insolvent. In the event that payment is not expected, zakat is not obligatory until the amount is received. According to the preponderant opinion, when it is received, the amount is subject to zakat for one year only.