Niṣāb threshold. Zakāt becomes due only when your net zakatable wealth meets the Niṣāb — equal to 20 mithqāl ≈ 85g of gold (the basis reported from the Salaf, used here by default) or 612.36g of silver as an alternative basis.
The rate. Zakāt on wealth is 2.5% (one fortieth) of your eligible net wealth.
Ḥawl — one lunar year. Wealth above Niṣāb must be held for one full Islamic (lunar) year before Zakāt is due on it.
What's included. Gold, silver, cash, savings, shares and investments held for growth, business stock, and recoverable debts owed to you.
What's exempt. Your home, personal car, clothing, furniture and tools of your trade. Debts you owe (due now) are deducted.
Note. This tool is an estimate. Scholarly opinions differ on details (e.g. jewellery in regular use, pensions, shares). Consult a qualified scholar for your situation.