How often do asymmetrical breasts usually even out?

Not often: Please remember that nobody has perfectly symmetrical breasts, so minor degrees of asymmetry are normal. If there is a great discrepancy, it can be treated by enlarging the smaller breast or reducing the larger. It is important to decide which breast is more normal (to the patient.) that is the one that should be matched.

Rarely: If you are past puberty and you breasts are uneven then the chances of this improving without intervention are slim to none and i think that slim may have just left town.