Boxer briefs can last anywhere from 6 to 12 months depending upon how often you wear them. In case you bring them to use on a regular basis then you should ideally change them after 6 to 7 months. Whereas, in case you wear them after a significant gap then you may replace them every 12 months. Moreover, there can't be a definitive period of time when your boxer briefs should last. Hence, a sign of damage or worn-out fabric can also be an indication that you must replace your boxer brief.