What is incumbent upon the questioner who paid zakat only on the money in his account for three or four years, instead of including all his money, including that in the market, knowing that he does not precisely remember the amount of money in each year due to the absence of an accounting ledger?

The zakat obligatory on institutions varies according to their activity. If the institution possesses commercial goods, then zakat on trade goods is due on them by evaluating them along with cash assets and collectible debts at the end of the hawl (zakat year), and one-quarter of a tenth (2.5%) is to be given. However, if its projects generate money without goods (such as land reclamation or software production), then the buildings, offices, cars, and machinery used by the institution are not subject to zakat. The money earned from these projects becomes subject to zakat if a hawl passes over it and it reaches the nisab (minimum threshold), and collectible debts are added to it, and one-quarter of a tenth (2.5%) is given. As for debts owed by insolvent individuals or those that cannot be collected, zakat is not obligatory on them until they are received, and then a new hawl begins for them. To simplify the matter, it is preferable to pay zakat on all profits at the end of the capital's hawl, and it is permissible to pay zakat in advance before its due time. As for past years for which zakat was not paid, it suffices to estimate the un-zakatized money based on dominant probability.