Zakat

6. Obligation to pay zakat on money [capital] used in trading:

"This money is that which is owned by a person, as a means of exchange [capital], intending to trade with it, earn a profit and, eventually, a living. It is obligatory, as a matter of ihtiyat, to pay zakat due on it, which is 2.5%, provided the following conditions are fulfilled:

1. The owner is adult and sound in mind.
2. The money should reach the bench mark of gold or silver. (For gold it is fifteen mithqal sairafi of coins and bullion - a unit of weight, equivalent to 4.608 grams), then every three mithqals thereafter. As for silver, it is one hundred and five mithqals, then every twenty one mithqals thereafter - Al-Masaail, p.221.
3. The lapse of one year on the [actual amount] of money, i.e. from the time it was intended for making a profit.
4. The intention to make profit should be constant the whole year, in that if the person changed his mind and appropriated some or spent some of it [money] on living expenses, for example, zakat will not become obligatory.
5. The ability of the owner to have the right of disposal over it for the whole year.
6. The amount of capital should be intact or there was an increase [profit] in it during the whole year. If, however, there was a decrease during the year, zakat will not become obligatory". Al-Masaail, p.226.