Another factor is how well you took care of the string. If you waxed them after each shooting session and didn't rub them on anything to fray them too badly the string willlast 2 seasons.Some people that shoot a lot but do notshoot competitive target replace them every year. Some guys replace after 1000 shots.

Overtime the spine on carbon arrows will "wear out" depending on how much you shoot and also if you shoot groups or one arrow per target. I don't think there' a set rule on the maximum number of shots per arrow. I think one guy on here said that he's still using the same arrows from 4-5 yrs ago.

However, if you don't feel comfortable with the arrows it's time for new ones. If the arrow has a crack in it or sounds funny when you flex it toss it. If you start to get erratic arrow flight that is not from the rest being out of tune it's time to change.