Generally speaking, the rulings of zakah vary according to the nature and the utilization of possessions. Houses and cars are no exceptions. The rulings on houses used for residency are different from those meant for trading, and the rulings on houses and cars for renting out are different.
Explaining the rulings and details of zakah on houses and cars, the eminent Muslim scholar and renowned da`iyah, Sheikh `Abdel Khaliq Hasan Ash-Shareef states:

Nowadays, there are huge investments in hotels, planes, ships, buildings, cars, etc.
Some people may believe that such issues were not handled by early Muslim scholars. In fact, this is a wrong idea. Scholars discussed the issue of renting houses and the zakah due on them.
The rulings on houses vary from case to case:

  1. If houses are owned for residence, there is no zakah in this case.
  2. If the houses are meant to be sold, they are liable to zakah on business (`urood at-tijarah), and in this case zakah is due on the value of the houses so long as the other conditions of zakah on business are fulfilled.
  3. If the houses are meant for renting, there is more than one opinion in this regard discussed below.

When we review the approaches of the fiqh books to the issue of zakah on rented buildings or vehicles, we will find two opinions:

  1. Zakah is due on the value of such buildings or vehicles (including planes, ships, and so on) plus their revenue. According to this opinion, the amount paid as zakah is 2.5 percent.
    In fact, this opinion is weak because it deems such possessions as `urood (possessions prepared for sale). This is far from the reality, since the above possessions are not meant for trading but for renting their services.
  2. Zakah is due only on the revenues yielded by such possessions. The advocates of this opinion are not agreed on the amount to be paid as zakah. There are two views on this:
    • the first view applies the ruling on money zakah to this case and, accordingly, the amount to be paid as zakah is 2.5 percent.
    • The second view applies the ruling on crops’ zakah and, accordingly, the amount to be paid as zakah is either 5 percent or 10 percent.

The first view holds that zakah is due on the revenues, not on the possessions themselves (i.e., the buildings and vehicles, etc.). This is based on the analogy with crops’ zakah, which is due only on the revenue. However, the same opinion specified the amount of zakah as 2.5 percent, which is the same amount due on `urood at-tijarah (business). It is to be noted that in `urood at-tijarah, zakah is due on both the capital and the revenues. Thus, the analogy employed in the first opinion, therefore, is questionable, for it is remarkable that when Shari`ah imposes zakah on both the capital and revenue, the amount of zakah is specified as 2.5 percent. On the other hand, when zakah is imposed only on the revenues, the amount of zakah increases (to 5 percent or 10 percent).

Shedding more light on the issue at hand, the prominent Muslim scholar Sheikh Yusuf Al-Qaradawi states:

If one builds or buys a building or a market to rent it, then such building is not considered `urood. Therefore, zakah is due on its revenues, not on its value. This is based on analogy with zakah on the revenues of arable lands.
As for the amount of zakah due, is it 2.5 percent like the zakah of money, 5 percent like the zakah on lands irrigated by machines, or 10 percent of the revenue, after deducting the expenses and the like? In fact, these all are possible. However, the opinion of 5 percent seems to be the most acceptable one. The first opinion (2.5 percent) is easier and more common among people, and it is somewhat passable.
Anyway, the Muslim is to spend the zakah on these revenues once he receives them (monthly for example). He should not wait until the year passes. This is based on the general provisions of Shari`ah and the analogy with crops, the ruling of which was mentioned in the verse (and pay the due thereof upon the harvest day ) (Al-An`am 6: 141).