Is Zakat calculated on the available liquidity or on the transportation profits for 12 months, taking into consideration the real estate bank loan employed in the project?

Zakat (definition) is obligatory on the profit gained from renting cars once a hawl (lunar year) has passed on each installment, after the money reaches the nisab (definition) (minimum threshold). It is permissible to pay zakat on the full rental income at the beginning of the hawl. As for what is spent on purchasing cars or other items during the hawl, zakat is not obligatory on it, because a hawl has not passed on it while it is in your possession. Regarding debts, there is a difference of opinion concerning deducting them from the wealth on which zakat is obligatory.