How much will my breast size change after augmentation surgery?

Generally speaking, breast implants will "drop" into the pocket that was created during surgery. The rate of breast implant "settling" may depend on factors such as size of breast implant pocket dissected, tightness of the overlying skin/muscle layers, and size of breast implant utilized. Normally, it takes about 3-6 months (for some patients longer) to see the final result. It is very common for one side to settle faster than the other.
Many of my patients report that as the swelling around the breast implants (for example, in the sternal area) decreases, they feel that their breasts appear more projecting. Also, in my opinion, the "drop and fluff” phenomenon does hold some validity; as breast implants “settle”, many patients feel that their breasts actually look larger. From the physiological standpoint, it takes many months ( and even up to one year) to see the final results of surgery. factors such as swelling, tissue contraction, skin redraping, implant shifting etc. come into play.  As breast implants "settle", they tend to round out the lower breast poles and the nipple/areola complexes shift upwards ("drop and fluff").
From the psychological standpoint, patients undergo an “adaptation period" during which time they get used to the changes that the surgical procedure has brought about. Severe emotional swings can also occur after any type of surgical procedure.Best wishes for an outcome that you will be very pleased with.

Breast implants tend to start dropping into place after 3 to 4 weeks. They usually will get to their final position in 6 to 12 months. One will usually drop faster than the other, and the shape may go through changes.  Please follow your Board Certified Plastic Surgeon's post op instructions. For example; we like message, but some surgeons will have you wait, or do it in a specific manner. Please let them know your thoughts and concerns. Jeffrey J. Roth, M.D., F.A.C.S.Board Certified Plastic SurgeonLas Vegas Plastic Surgery

Two things happen and seem paradoxical. As as the swelling goes down there will be some shrinkage but at the same time as the muscle relaxes your breast projection grows. In general the breast shape and size proportionality improves..Breast implants initially after surgery when placed in a submuscular position often give superior fullness that corrects itself with time, the "fluff and drop" phenomena. In reality the pectoralis major muscle takes a while to adjust its size to accommodate the implant as well as occasional muscle spasm which keeps the implant projection higher than its final resting shape. Additional variables include:laxity of skin, size difference during prior pregnancies, position of implant,size of muscle, and size of implant.As the muscle relaxes the projection of the implant often increases and the breast shape improves. Massage and use of a superior placed elastic strap can often make this process go faster.