Is Zakat obligatory on gold that is used or gold that is saved, and how is it paid and what is its amount, and is it necessary to pay it for past years?

Scholars differed regarding the obligation of zakat on used gold, and it is preferable to pay it to avoid disagreement. As for gold prepared for trade or savings, zakat is obligatory on it if it reaches 85 grams or more, and one-quarter of one-tenth (2.5%) of its value is to be given. To calculate this, the amount of gold is multiplied by the price per gram, and 25 Riyals are given for every thousand Riyals. As for previous years in which zakat was not paid, the quantity of gold for each year must be estimated, and zakat calculated according to the price of gold in each respective year. The equation used: (weight of gold × carat type × 2.5%) × price per gram of pure gold on the day zakat became due, divided by 24.