Answered by Shaykh Amjad Rasheed
I pay money to the mosque for its maintenance and to help pay off its debt, so does that money count as paying zakat?
Bank interest is unlawful (haram) money when a result of riba-based arrangements. As such, it is not part of one�s wealth even when placed in one’s account. Rather, it remains the property of its right owners.
Given this, no zakat is due on the bank interest, because it is not your property.
It is not permitted for you to use money that is not yours. Rather, if you are are able to return it to its rightful owners, you must do so. When you cannot return it to its rightful owners–as is the case with bank interest–then it is considered lost wealth’ (amwal da’i`a) that must be directed to the general interests of Muslims, such as the poor, students of knowledge, mosques, and the like.