How is zakat on wealth calculated for a company whose capital has increased over three years: is it on the capital or only on the profits?

The questioner did not clarify the company's activity to determine the type of Zakat due: whether it is on the capital along with the profit (like commercial companies), or on the profit only (like service companies). In both cases, Zakat is obligatory for every past year in which the wealth reached the nisab. Each shareholder pays Zakat on their share if a year has passed over it and it reached the nisab by itself or when combined with other assets.