What is the zakat threshold for shares purchased at infrequent intervals over more than two years, the value of which has decreased to a quarter of their original value?

Zakat is obligatory on the value of some stocks but not others.

Stocks on which Zakat is obligatory are subject to Zakat after one year has passed since they reached the nisab, and a quarter of one-tenth (2.5%) of their value is to be paid at the time Zakat becomes due.

As for stocks purchased later, if their capital originated from the first stocks, they are subject to Zakat along with them, and their hawl (zakat year) is tied to theirs. However, if their capital did not originate from the first stocks, Zakat is not obligatory on them until a hawl has passed over them. It is permissible to combine them with the first stocks and pay Zakat on all of them when the hawl of the initial capital is complete, or to wait for the completion of the hawl for each new batch of stocks. It is not a condition for the new capital to reach nisab on its own, as it follows the initial capital in terms of nisab and is of the same kind.