This is a pet peeve of mine so forgive me. Every year we get bows in right before season with the strings broken in two (one came in tonight in fact) and usually we're told they're 4-6 years old. My thinking is how much is your health/life/hunt worth? If your string breaks there's no telling what or who will get hurt and how seriously. That said, I make my own so change them every year. I know not everyone makes their own and it can be an added expense but I would recommend changeing them at least every other year depending on the amount of shooting you do.