I bought the right cup size, but it is way too big because my breasts still bounce around A LOT when I'm running or doing any aerobic activity. I've tightened the straps, the band, but it has no effect. I've not worn a B since high school, and I've been a C through weight loss & gain (for a while I bordered on D, but never down from C), so I know I'm not a B. Anyway, it's comfortable but ineffective for support while exercising.