How is the value of Zakat calculated on saved money that has reached the nisab and is increasing monthly?

The zakat on salary has two conditions: reaching the nisab (minimum threshold) and the passing of a full hawl (lunar year) on the money. The easiest method is to pay zakat on the portion of the salary that has remained after a full year has passed since it reached the nisab. For example, if someone has an amount reaching the nisab from their Ramadan salary, they would pay zakat on it the following Ramadan. If they wish to calculate a separate hawl for each salary amount they save, they may do so, but the first method is easier and more beneficial for the poor.