How is the zakat calculated for a sum of 90,000 Saudi riyals in a bank account that fluctuates, and is it permissible to give zakat to a friend without informing him that it is zakat, in order to help him pay the rent, knowing that there are those who are in greater need?

Zakat must be paid on the bank balance if it reaches the nisab (minimum threshold) and a full lunar year (hawl) has passed on it. Zakat is calculated by combining the balance with any cash or business assets the person owns. If the balance falls below the nisab before the end of the hawl, then no zakat is due on it. Acquired wealth is subject to zakat as part of capital if it is a profit from trade. As for salaries, they are subject to zakat when a hawl passes on each installment, or one can pay zakat on all of it when a hawl passes on the original capital, which would be more beneficial for the poor. It is permissible to give zakat to your friend if he is deserving, and it is not required to inform him that it is zakat unless he would not accept it. It is preferable to give zakat to those in greater need.