Praise be to Allah.
With regard to the mudaarabah and muraabahah shares, you should pay zakah on both the principle and the profits, when one full year has passed on the capital. With regard to the shares which are held in agricultural, real estate and industrial companies, zakah is due on the profits if they reach the nisaab (minimum amount) on their own or when added to others, and one full (hijri) year has passed. The rate of zakah is one quarter of one tenth, i.e., 2.5 %. With regard to the shares, zakah is not due on them if they are not available for sale. But if they are available for sale then zakah must be paid on them and their profits when one full (hijri) year has passed, as with all other trade goods. If the agricultural company produces grains, dates or grapes then the prescribed zakah must be paid on them if the amount of each of them reaches five wasq or more. And Allah is the Source of strength. May Allah bless our Prophet Muhammad and his family and companions, and grant them peace.