I believe it runs true to size, but I choose to size up by 1 because I have 40DDD and a mom pouch and I wanted a loose fit, it's comfortable around my breast, belly and hips like I wanted, if your smaller in the breast, belly, hips and bum, and you normally fit a 16/18 a 2x should fit you perfectly, don't size up unless you want it to be non form fitting. I do have to alter the shoulder straps because I sized up to a 3x. All in all, I like it. I'm 5'3 48-40-49 198lb.