How do I calculate Zakat on jewelry that has both gold and silver in it?

The best route is to figure out the amount of gold and silver individually (their weight) and then calculate the Zakat value accordingly.

Gold and silver can be valued at its resale value by a jeweler or you can multiply the number of grams (of gold or silver) you own by the current market value. 

In order to calculate Zakat on silver and gold you must take into consideration the following:

• The purity of the gold and silver within the jewelry.
• 24K gold is considered pure gold
• To find the purity percentage of your gold, you must divide the karat value of your gold by 24 (the karat value of pure gold)
• The weight of the gold and silver within the jewelry.
• This is the true grammage of the amount of gold or silver within the jewelry and is based on the purity percentage
• To find the true grammage of your gold or silver, you multiply the total weight of gold or silver in your jewelry by the purity percentage
• The value of the gold and silver within the jewelry.
• This is determined by the current value of gold and silver on the Zakat calculation date

For example, if you have 100g of 18K gold, you would calculate as follows:

• Purity Percentage = 18/24
• True Grammage = 100 x Purity Percentage
• Value = True Grammage x Current Value of Gold (per gram)
• Zakat Due on Jewelry = Value x 2.5%