It depends on the kind of investment you make. Mainvest offers two types: debt and equity-based.
If the investment is debt-based (a.k.a. you have a Revenue Sharing Note), the most you can generally receive is your money back, plus interest. The interest on Revenue Sharing notes is a set amount known as the investment multiple and detailed in the offering terms of each business.
If the investment is equity-based, you have the potential to earn more (or less) depending on the success of the business you hold equity in.
Remember, every investment entails risk and Mainvest does not make recommendations on the types of investment you should pursue.