Add what you own, take off what you owe now, and measure the rest against the nisab. Type in today's gold and silver prices from any source you trust — the page looks nothing up and sends nothing anywhere.
Use any currency, as long as every figure is in the same one. Prices are typed in, not looked up — nothing on this page is sent anywhere.
Enter the silver price per gram to measure against the nisab.
Zakat is due on wealth that can grow or be spent: cash, gold and silver, money owed to you that you expect to recover, goods held for sale, and investments. It is not due on the home you live in, the car you drive, your clothes and furniture, or the tools of your trade. The total, less debts falling due, is compared with the nisab; if it has stayed at or above that line for a whole year, a fortieth of it is due.
The details sit in the guides: nisab and who has to pay, zakat on gold and who can receive zakat. Why the rate becomes 2.577% on a Gregorian year — and what paying every 1 January quietly misses — is measured in zakat on a lunar or solar year.