Is zakat obligatory on the remaining amount of money allocated for buying a car after purchasing it for less than the allocated amount, and how is its zakat calculated?

Zakat is obligatory on wealth that reaches the nisab (minimum threshold) after the passing of a full year (hawl), whether it is saved for buying a car, a house, marriage, or anything else. This is because Zakat is a right of the poor. It is obligatory upon you to pay Zakat on all wealth that a full year has passed over, whether it is saved for buying a car or for other purposes.