All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
In principle Zakat has to be paid from the jewelry itself and not cash money according to its value. One has to pay 2.5 grams Zakat from every 100 grams, which means 2.5%. However, if one wants to pay the Zakat as cash based on its value instead of giving out the gold itself, then he has to find out its value in the market. What matters is the price of the raw gold and not the refined gold (which is usually more expensive) and then one has to pay 2.5% Zakat from its value.
Therefore, Zakat is neither calculated according to the value of the new gold nor according to the price with which one has bought the gold, rather it should be calculated according to its value in the market when Zakat becomes due.
Allaah knows best.