A quick way to tell if you overpronate as well as gauge how severe your pronation issues are, simply take a look at the wear and tear on your running shoes. A runner that has an even gait wears down their running shoe evenly on the toe box and heel. If you overpronate, your sole may look a little different.
Overpronators put more weight on one side of their trainers. If you find that the side of the toe box under your big toe and the side of your heel are worn down unevenly, you overpronate. If they are worn down on the opposite side, you underpronate.