Do we have to give Zakah to the amount which we give as Sadaqa? In business we have to give Zakah to capital plus profit. What if business is a loss? Do we then have to give Zakah on the capital? If we have 2 cars, and the second car was bought for selling, do we have to give Zakah after receiving the money from selling the car immediately or after one lunar year?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

1) Sadaqah (optional charity) is not considered as paying Zakah.  Zakah is an obligation, thus one should give it with the intention of Zakah.  The Prophet (Sallallahu Alaihi wa Sallam) said: “The deeds depend on intentions, and every person will get the reward according to what he intends.” [Reported by Imam Al Bukhari]

If you had already paid with the intention of charity then it no longer could be considered as Zakah.

2) If one suffers losses in his business and his amount decreases to the extent of not reaching the limits of Nisaab then no Zakah is due on him.

3) If the person possesses a car against some payments with the intention of business, it comes under the ruling of trading goods and thus he has to pay the Zakah every year on the value of the car without any delay.  If he possesses without any payment or without the intention of business, and later on intends to do business in this car then  Zakah becomes due only when one lunar year passes after selling the car and keeping the amount for one year.

Allah knows best.