Is zakat due on gold after a year has passed since its purchase, or on the same date as the original zakat payment for the cash amount that was converted into gold?

Gold purchased for trade is subject to zakat (definition) at the same time as the money used to purchase it, because money is a price that takes the place of gold and silver, and purchasing it with money does not alter its hawl (zakat year). It is stated in "Al-Mubdi' Sharh al-Muqni'": "And the hawl of some prices builds upon others."