How is the Zakat calculated for an apartment bought for investment, rental, and then sale, with monthly installments being paid, at its different stages: before and during rental? Is Zakat due on the value of the apartment or only on the rental income? And how is its market value estimated?

Zakat is obligatory on an apartment that is still under construction, which you intend to sell after four years and rent out for two years before selling it. This is because it is considered a trade commodity intended for profit, even if the intention to rent accompanies the intention to sell.

Zakat is calculated annually based on the apartment's value at the end of each lunar year (hawl), and the zakat amount is one-quarter of one-tenth (2.5%). If the property was purchased with saved money, the hawl for zakat is based on the hawl of that original money, and a new hawl does not begin upon purchasing the property.

As for the apartment's rent, zakat becomes obligatory on it if you receive it in advance and it remains with you for a full hawl. If it is spent before the hawl ends, there is no zakat on it. If you receive the rent at the end of the hawl, it is subject to zakat immediately.