Is Zakat obligatory on gold and money that have reached the Nisab and on which a full Hawl (lunar year) has passed, despite uncertainty about the date of the Hawl, and the existence of other money on which a Hawl has not yet passed; and is it permissible to pay Zakat in advance on all the money, and how is the Zakat for the coming year calculated?

Zakat is obligatory on gold if it reaches the nisab (minimum threshold) and a full lunar year (hawl) passes over it. A strong presumption that a full hawl has passed and that it has not fallen below the nisab is sufficient. Newly acquired gold begins a new hawl from the date of its possession, and zakat is only obligatory on the amount that has completed its hawl. It is permissible to pay zakat in advance before the completion of the hawl. As for the zakat on salary, it can be added to other funds and zakat paid on it when their hawl is due, or a separate hawl can be set for each salary payment individually. The easiest and most beneficial method is to pay zakat on all savings (gold, salary, cash, trade) when the hawl is due for the first nisab you possessed.