How is the Zakat calculated on hoarded gold whose weight increases every two months due to the addition of more gold to it?

If the accumulated gold reaches the nisab (definition) (threshold) by adding newly acquired gold to it, then the hawl (one lunar year) begins from the day it reaches the nisab, and zakat (definition) becomes obligatory if it remains until the completion of the hawl.

However, if the accumulated gold has already reached the nisab and you acquire additional gold, then if the newly acquired gold is a product of the initial nisab, it is zakatable along with it. If it is not a product of it, you have the option to either zakat it with the initial gold or assign it an independent hawl.

Scholars have differed regarding newly acquired wealth of the same type as an existing nisab that has completed its hawl, but is not a product of its growth. The Shafi'is and Hanbalis hold the view that it is added to the initial amount for the nisab calculation, but not for the hawl. Each portion is then zakatable when its own hawl is completed.