Question: Do we need to give tax (zakat) from the money in participation banks? Should the calculation be made from the sum or the revenue of it?
Money deposited on a profit-loss sharing account is subject to tax (zakat) as a whole. It should be given tax from the sum of it.
If 10.000 $ is deposited on a profit-loss sharing account and it reaches 10.600 $ at the end of the year, the calculation should be made from the total amount:
10.600 / 40 = 265 $ (zakat)