How can one pay zakat on a sum of money deposited in a bank, to which salary is added monthly over ten months, after the original sum was paid zakat on in the previous year?

Bank deposits are subject to zakat (definition) on both the principal and its profits at the end of the year (hawl). The salary added to the deposit is subject to zakat in one of two ways: The first (and easier) is to pay zakat on all deposited funds, including the salary, on the original hawl date of the deposit, even if the salary alone has not reached the nisab (definition). The second (and more difficult) way is to allocate an independent hawl for each amount of salary saved. Zakat calculation must be done according to the Hijri calendar, and the profit must be zakated along with the principal.