The nisab calculated with the silver standard is significantly lower than its gold counterpart. This is because the value of silver has plummeted since the time of the Prophet (peace be upon him).
There are arguments for using either nisab value. Many scholars say that it is better to use the silver nisab since it will increase the amount of charity distributed; others say that the gold nisab is closer to the nisab in use at the time of the blessed Prophet (peace be upon him).
However, if your assets consist entirely of gold, you must use the gold nisab, and similarly, if they consist entirely of silver then the silver nisab must be used.
As long as you are in possession of wealth above the nisab threshold at the beginning and end of the zakat year, zakat will be payable, even if your wealth dipped below the nisab for most of the year.
If a person possesses wealth exceeding the nisab threshold, but has to pay rent, purchase food, clothing, etc., for themselves and their dependants, then these costs may be deducted from one’s wealth.
If, after deducting these costs, the remaining amount is less than the nisab at the end of the zakat year, then no zakat is payable
The zakat year begins on the date on which you were first in possessions of wealth above the nisab.
This will be your seed date, whenever it comes around you will have to calculate zakat, irrespective of any fluctuations in the amount of wealth in your possession.
The only situation in which your seed date will change is if you were to become totally bankrupt and lose all your assets and belongings. In this situation, your new seed date will begin when you are once again in possession of wealth above the nisab.
If you are not sure of your seed date, then estimate it to the best of your ability.
