If someone has gold that reaches the Nisab, and its market value increases two months before the due date of the Hawl (lunar year), is the Zakat to be paid on the original purchase value or on its value after the increase?

Jewelry intended for savings is subject to Zakat if it reaches the نصاب (minimum threshold), whether by itself or when combined with money or trade goods. Zakat is due on its value at the completion of the hawl (one lunar year), not at the time of purchase, even if its value increased a few days before the hawl. The Zakat rate for gold is a quarter of a tenth (2.5%).