After six months to a year of regular wear, your tee enters its mid-life. The fabric starts to soften, which is good—it feels broken in. But you'll also start to see signs of wear:

• Collar stretching: The neckline might start to look like a boat neck. That's a sign the ribbing is losing its elasticity.
• Fabric thinning: Hold the tee up to light. If you can see through the fabric easily, it's thinning out.
• Pilling: Little balls of fuzz forming on the surface. This is more common on lower GSM tees, but it can happen to any tee with friction.

At this point, you might still get a year or two of wear. But if the collar is so stretched it looks sloppy, or the thinning is in high-friction areas (underarms, elbows), it's time to think about replacement.