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.

Current, savings and money held for others you may use.
Weight of the gold content. Schools differ on jewellery worn regularly — see below.
Held to trade: full value. Held long-term: many scholars use the zakatable share of the company's assets.
Only what is payable now or this year — not the full balance of a mortgage.
Zakat due

Enter the silver price per gram to measure against the nisab.

What counts, and what does not

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.

Questions

How much is zakat?
2.5% of zakatable wealth held above the nisab for a full Hijri year. If you keep your zakat year by the Gregorian calendar instead, the rate is 2.577%, because the solar year is about eleven days longer.
Should I use the gold or the silver nisab?
Both are classical. The silver nisab (612.36 g) is far lower in money terms, so more people owe zakat under it and more reaches the poor; many scholars and the Hanafi school favour it for cash. Others use gold (87.48 g) as closer to today's value of the original threshold. The calculator lets you pick.
Is there zakat on jewellery I wear?
The Hanafi school says yes, on gold and silver jewellery whatever its use. The Maliki, Shafi'i and Hanbali schools generally exempt jewellery worn in normal, customary amounts. If you follow the latter view, leave worn jewellery out of the gold and silver weights.
Do I deduct my mortgage?
Not the whole balance. Most contemporary scholars allow only what is due now or within the coming year — the instalments you actually owe — to be deducted, otherwise almost no homeowner would ever reach the nisab.
Where can my zakat go?
Only to the eight categories named in the Quran (9:60), headed by the poor and the needy. The categories, and who counts as poor when they have an income, are explained in the guide to who can receive zakat.