How to calculate the monthly zakah on a bank deposit if it reaches the nisab

Question:
A man saves a deposit in the bank that equals the nisab for zakah every month, and so on. How does he pay zakah on it?

Answer:
He should look at it, write down what he deposits, and make a clear written mark or otherwise. When the lunar year (hawl) passes over this specific item he has designated and marked, he pays zakah on it. However, if the lunar year does not pass over it—he spends this, then replaces it, then spends it before the hawl completes—he owes nothing, provided the saved deposit does not complete a hawl. Rather, whenever he deposits something, he consumes it and then replaces it; he owes nothing.

Question : No, he intends that whenever he deposits the nisab, he adds to it in the following month, and the one after that, and so on. The last installment will not have a hawl pass over it, will it?

The Shaykh: If he preserves that, he pays zakah on everything, until the hawl passes over it.

Question : So, does he pay zakah every month on this?

The Shaykh: Yes, whenever the hawl passes over it, he pays zakah, as long as he preserves this. And if he pays zakah on the whole amount, it becomes an early payment of zakah on the last portion, and there is no harm in that.