As with all things in economics, it’s not a free lunch. The cost of credit has already been priced into everything you buy. In this case, you can choose to make a small amount of money in exchange for some headache of making sure payments go on time, or leave it alone. If everyone eventually takes 2% rewards, instead of using debit cards and plain cards, the cost of credit in your purchases will rise from about 1.8% to 2.8%.