This is one way they make money. Robinhood is free because it makes interest on the money you ACH transfer in that sits while you make your decision on what to

This is one way they make money. Robinhood is free because it makes interest on the money you ACH transfer in that sits while you make your decision on what to buy. They have a big bank account holding all of the user's funds and get interest on it. Of course they cannot make interest on the money traded for a stock though.