Is money deposited in an investment account that guarantees monthly profits of 4% without loss permissible or impermissible?

For an investment project to be permissible, two conditions must be met: the project must be Islamically permissible, and the capital must not be guaranteed. If the bank guarantees the investor against loss, then the investment is impermissible because it constitutes usury (riba). It is also a condition that the share of both the capital owner and the investor be a fixed percentage of the profits, not of the capital. If the promised profits are estimated relative to the capital, then the transaction is an usurious loan and not a legitimate Mudarabah (definition) (profit-sharing partnership).