How is zakah calculated on accumulated funds from which expenses are paid?

Question: If a person has a source of income that comes to him bit by bit, such as an employee or a merchant, and he spends from it without knowing when the lunar year of possession has passed, what should he do regarding zakah?

Answer: It is obligatory for such a person to record the times when money comes in and to keep track of them so that he knows the lunar year of possession for zakah. He should set aside a specific amount for expenses, and whenever it runs out, replace it with other funds, so that the matter of zakah does not become confused for him. However, if he is generous enough to pay zakah on the total amount of money accumulated with him each year, considering the first money that reached him, there is no blame on him, and he does not need to record the times of income. Because if he pays zakah on the whole, his conscience is fully cleared. Anything in excess of the zakah is voluntary charity, and the reward for charity is well known and great. May Allah make us and you among those who give charity.