So many clients ask the question, "how often should I change my running shoes"? A pair of running shoes loses approximately 50% of its ability to absorb ground reactive force after 300-500 miles. The worn out shoe and lower ground reactive force are transferred into your knee and increase risk factor of Illiotibial Band Syndrome (ITBS).
Running shoes can be expensive, so be sure to research the highest quality shoe for the best price. Don't be cheap and don't put it off. You will be sorry and your body will show signs of uncomfortable pains throughout your run. You are putting yourself at risk for long term injures. I can always tell when it is time to buy new sneakers. My hips will ache, my knees are sore and my feet hurt throughout the run. Be sure to listen to your body and do not prolong the purchase, this is an investment you will need to consider as a runner.