How is the zakat calculated for gold and foreign currency for that which has been held for a full year (hawl) and that which has not? And when is the zakat due on trade goods, such as an apartment bought in installments? And how is the zakat calculated for saved gold when it is sold: Is it on the profit or the entire amount, and at what price is it valued?

If someone possesses wealth that reaches the nisab (minimum threshold for Zakat) and acquires more wealth of the same kind during the hawl (Zakat year), they should add it to the existing wealth and pay Zakat on both if the new wealth is a product of the original. If it is not a product of the original, they have the option to combine it with the first wealth and pay Zakat on both when the hawl of the first wealth is due, or to start a new hawl for the newly acquired wealth. If the original wealth does not reach the nisab, but the nisab is completed by the newly acquired wealth, then the hawl for Zakat begins from the date the nisab was completed. Therefore, if the questioner has gold and paper currency, and acquires one of them during the hawl of the other, and the first one had reached the nisab, they can combine the Zakat of the second with the first and pay Zakat on both together (which is an advancement of Zakat and permissible), or pay Zakat on each according to its hawl. The first method is easier and more beneficial for the poor. If the first wealth was below the nisab and it was completed by adding the second, then Zakat on both should be paid when the hawl is completed from the date of acquiring the second wealth that completed the nisab.