A pair of standard running shoes will last somewhere from 300 to 500 miles. For our average customer, this means replacing shoes around every six months. However, there are a lot of factors that will influence how often your shoes need to be replaced. For example, a lightweight trainer will last fewer miles than a traditional running shoe. What you do in your shoes, the surface on which you run, the frequency of use, and many other factors will affect the length of time that your shoes will last. If you wear your running shoes to work every day and stand on a hard surface, then it is not unusual for your running shoes be worn out in as little as two months.
When in doubt, listen to your body. If your back, hip, knees or ankles are saying "I need new cushioning!" or "I need new support!", then do what is best for you.