Is Zakat obligatory on money deposited in banks, and is it obligatory on the principal or the returns or both, and how is Zakat calculated on monthly deposits?

Funds deposited in Islamic banks are subject to Zakat on both the principal and the profit. The entire fund is subject to Zakat when a full year (hawl) has passed since the acquisition of the first nisab (minimum taxable amount), or a separate hawl can be designated for each independent fund, with the hawl of the profit following that of its principal. As for funds deposited in interest-based (usurious) banks, Zakat is obligatory only on the principal amount. There is no Zakat on the interest-based profit because it is ill-gotten wealth (mal khabith) that must be disposed of by giving it to the poor, and it is not permissible to count it as part of Zakat. It should be known that depositing funds in interest-based banks is forbidden.