How zakat on gold and silver works
Zakat is an annual obligation of 2.5% on wealth that has stayed at or above the nisab for one full lunar year (hawl). The nisab comes from the hadith: 20 mithqal of gold and 200 dirhams of silver, which most scholars today put at 85 grams of gold and 595 grams of silver. Many South Asian scholars use 7.5 tola (87.48 g) and 52.5 tola (612.36 g).
Gold and silver by purity
Only the pure metal counts towards its value. A 10 g 22K bangle contains 9.16 g of gold; 10 g of 18K contains 7.5 g. The calculator converts each karat for you and values it at today's price per gram — the metal value, not the shop price.
What to include
Add cash at home and in the bank, savings, gold and silver, the zakatable part of shares and funds, business stock valued at its sale price, and money you expect to be repaid. Subtract debts and bills that are due now. Your home, car, furniture and personal belongings are not zakatable.
Jewellery
The Hanafi school counts all gold and silver jewellery. The Maliki, Shafi'i and Hanbali schools generally exempt jewellery worn for normal personal use but count jewellery kept as savings. Untick "Include jewellery I wear" and enter how much of your gold is worn to follow that view.
This calculator is a guide to the arithmetic, not a religious ruling. For your own situation, please ask a qualified scholar or your local zakat authority.