How long your underwear lasts is really up to you. While the ball(s) are in your court, you're better off clearing the bench no later than twice a year, and that's assuming you have more than seven pairs on deck. Considering it's something that you're wearing on a regular basis, you're looking to have multiples on multiples. The sign to throw them in the trash bin instead of the laundry bin? Fading, over-stretching, and the obvious, irremovable stain are key signs you're better off copping a new three-pack.