Q: If one has given their Zakah in advance for forthcoming years and on the anniversary realises this amount was above his actual Zakah total, can one consider this surplus amount to be a Zakah payment for subsequent years?
A: If a person has donated their Zakah in advance either for the current year or the forthcoming year(s) and on the Zakah anniversary one realises that one has donated more than what the Zakah calculates to be then the extra Zakah paid can be considered to be for subsequent years provided the Zakatable asset for which the Zakah is to be considered is of the same genus as that for which the Zakah has been paid. If it is of a different genus then it cannot be considered for future years. Gold and silver [and modern] currency and trade stock are considered to be of the same genus whilst goats and camels are separate genera.