A lot also depends on the type of material it is made out of, with the new materials strings are being made from they will last a lot longer. I had one of my last bows with a string that lasted 8 years on my hunting bow and changed my string on my tournament bow once just for giggles and that string had 1,000's of shots on it. Take care of them, inspect for nicks and freys and you'll be okay. However, the most critical part on the string is under the serving were you nock you arrow, this is the biggest pinch point and gets the most action. Most strings I've see break have broken there, have your serving changed at least once every two seasons just be sure about the strands under your serving.