How is the Zakat calculated for a house that was bought for future residence and temporarily rented out, and another house that was bought for investment but its construction is not yet complete?

A house designated for dwelling is not subject to Zakat, based on the Prophet's (peace be upon him) saying: "A Muslim is not required to pay Sadaqah (Zakat) on his slave or his horse." This includes assets held for personal use. As for the monthly rent derived from it, Zakat becomes obligatory on it if it reaches the nisab (minimum threshold) and a full hawl (lunar year) passes, by combining it with other zakatable assets if any exist.

Regarding the second house designated for investment: if the intention is to rent it out, its ruling is the same as the first house. However, if the intention is to sell it and invest its price, then it is considered a trade commodity. Its value should be assessed at the end of each hawl, and 2.5% of its value is to be paid as Zakat annually.

Concerning debts, if you possess non-zakatable wealth that covers them or part of them, then allocate it to offset the debt. Subsequently, subtract the remaining debt from your zakatable assets and pay Zakat on the remainder.