Add up the zakatable wealth you have held for a full lunar year (cash, savings, gold and silver, trade goods), subtract debts due now, and compare the total with the nisab.
If net wealth ≥ nisab, zakat = net wealth × 2.5%. The gold nisab is the value of 85 grams of gold at today's price.
With 12,000 in savings and gold at 25 per gram, the nisab is 85 × 25 = 2,125. Since 12,000 is above the nisab, zakat is 12,000 × 0.025 = 300.