As a rule of thumb, 6 months, but it all comes down to a couple of factors:
- How often you train in it each week
- Intensity of training
- How often you wash your sports bra and how
When I was training for my half marathon I had to replace every 3 months. I could feel they weren't giving my F cups the support anymore.
According to research conducted by Portsmouth University, the more you exercise, the more the elasticity in your sports bra stretches. So a well-loved bra won’t offer you much in the support department—and this can speed up the inevitable sagging process, no matter your cup size.
So remember, if you’re exercising more than three times per week, for more than 45 minutes per session, retire your sports bra after six months.
Also, look for signs of wear and tear. If it’s just a tad too comfy (meaning the support’s just not there anymore), if the band at the bottom seems looser or if you notice a bit more bounce as you’re exercising, it’s time to go shopping.