The basic principle is that when a Muslim's wealth reaches the nisab (minimum threshold) and a full lunar year (hawl) has passed, zakat becomes immediately obligatory. It must be paid without delay.

The Permanent Committee for Scholarly Research and Ifta' was asked about paying zakat in installments after its due date. They ruled that this is not permissible. Zakat is a right that belongs to the poor and other specified recipients, and delaying it without a valid Shar'i (legal) excuse is considered withholding this right from those who deserve it.

They stated: "It is obligatory to pay zakat immediately once it becomes due, and it is not permissible to delay it unless there is a legitimate excuse according to Shari'ah, such as the money not being on hand, or if there is a calamity that has befallen the zakat payer that makes it difficult for him to pay it on time."

Therefore, paying zakat in installments after the hawl has passed is only permissible in cases of genuine necessity or for a significant reason, not for mere convenience. For example, if a person's wealth is tied up in assets that cannot be immediately liquidated, or if paying the entire lump sum at once would cause them significant, demonstrable financial hardship, then there may be a concession. However, the default ruling is immediate and full payment.

It is worth noting that it is permissible to pay zakat before it is due. A person may pay their zakat for the upcoming year in monthly installments. Once the zakat due date (the end of the hawl) arrives, they would reconcile their payments and pay any remaining balance immediately.