When do boobs stop growing?

Breast growth: Your breast will stop to grow once puberty is over by age 18-20. However, since breasts consist mostly of fat cells, although the number of fat cells won't increase after that, your breasts may get bigger if you gain weight, use birth control pills or get pregnant only because the fat cells get "fatter". Likewise, if you lose weight, your "boobs" can get smaller because the fat cells "shrink".

Breast size is : likely to ^ w puberty, pregnancy, breast feeding & possibly prior to your period. SOME Oral contraceptives may ^ breast size in SOME women, SOME OF THE TIME. Breast size often increases with weight gain. Thus - there is no specific time.