no. 3010 for the year 2005 which includes the following:

How is zakat calculated for a joint-stock company with capital investment, working capital and annual profits?

Zakat due on a company, whether a sole proprietorship or a partnership

It is paid upon the working capital and annual profits (if the nisab is reached). Zakat equals one quarter of the tenth (i.e. 2.5%) and is paid after one lunar year passes. No zakat is due upon the capital investment.

Allah Almighty knows best.