About Zakat calculations...
you can see more information here
When does zakat become obligatory?
Let's say for example the current gold nisab today is 12000 USD
Zakat becomes obligatory on a person once THREE conditions are ALL satisfied. Not one of them, not two of them, but ALL of them:
1. The person is a Muslim
2. The person's total wealth exceeds the nisab threshold, in this example, has more than a total of 12000 USD
3. The person's total wealth sustained the nisab threshold for a whole lunar year, in this example, has had more than a total of 12000 USD for a whole lunar year
If all these conditions are true, then Zakat becomes obligatory and falls due
How is Zakat calculated?
Simple. You multiply 2.5% by your current total wealth. That's it :)