The permissible method is that when one year passes, he estimates the commercial commodities according to the market price at that time [of estimation] (Part No. 9; Page No. 320) regardless of the purchase price. If he estimates the commercial commodities which have been in his possession for less than one year, and adds the due amount of these commodities to the amount of the commodities that he kept for a complete year, there will be no harm. Paying Zakah in advance is permissible and beneficial for the channels of spending Zakah.May Allah grant us success. May peace and blessings of Allah be upon our Prophet Muhammad, his family and Companions!