The Nisab (threshold) for Zakat is 7.5 Tolas of gold (87.5 grams) and 52.5 Tolas of silver (612 grams).
If you possess either of these items in the mentioned quantity, or both items in smaller quantities whose combined value equals the value of 612 grams of silver, or if the value of your trade goods equals 612 grams of silver, or if your cash money equals 612 grams of silver, or if the combined value of your gold, silver, trade goods, and cash equals 612 grams of silver, then you are considered Sahib-e-Nisab (eligible for paying Zakat).
After one lunar year has passed on these possessions, it becomes obligatory upon you to pay Zakat.
After one lunar year has passed, determine the value of all the gold, silver, cash, and trade goods you possess, and add them all together.
Include in this amount any money you have lent to someone or any other money owed to you.
Deduct from this amount any debts you owe to others or any other money you owe them.
Then, calculate 2.5% of the resulting total amount. This amount is your Zakat.
You can pay this amount in one lump sum or in installments as per your convenience, both are permissible.
Zakat should be calculated based on the completion of a lunar year. For example, if you first became Sahib-e-Nisab in Muharram or Ramadan, calculate your Zakat every year in the same lunar month.
Ensure that you calculate your Zakat in the designated lunar month. Note down the obligatory amount in a diary, and pay it in installments as per your convenience. There is no issue in doing so.