Do breast implants look bigger if they are over the muscle?

Over time, the size will be about the same for under and over the muscle, however, under the muscle avoids the edge look and has less rippling and sagging. If you have minimal tissue or need a lift, placing the implants behind the muscle will give a better long term look.

Hello
and thank you for your question. There are advantages
and disadvantages to each technique and there is no one right answer that can
be given. Generally speaking, submuscular placement of the implant is
associated with less risk of capsular contracture, more natural upper pole
slope and less rippling/implant visibility. As there is a layer of muscle
separating the implant from the breast tissue, there will also be less interference
with mammograms. I would discuss all of these
with a board-certified plastic surgeon prior to making your final
decision. 
Best
wishes and good luck,
Pejman
Aflaki, M.D. Johns Hopkins-trained double board-certified plastic surgeon

Breast implants placed on top of the muscle (subglandular) tend to look less natural than implants placed under the muscle. Think of placing implants on top of the muscle vs. under the muscle as if you were to place something under a sheet vs. a blanket. The three reasons I usually place implants under the muscle: appears more natural, less likelihood for capsular contracture, and perhaps less likelihood to interfere with mammograms. Definitely discuss your concerns and questions in person with a board certified (ASPS Member) plastic surgeon.