Boxers achieve most of their growth in six months. They will pick up additional weight for the first couple of years. The old way of predicting a dogs size by the size of the puppy's feet is really pretty acurate.
How Long Does Boxer Dogs Grow?
6-8 months you dog will get his height and length close to where he will be as an adult.he will fill out with weight all the way to 2 yrs maybe a little longer on some.our male is 87 lbs which is big for a boxer but hes big boned and not fat at all weve also got a large female at 75 lbs.gl with your boxer 
They grow until there 1year old then they stop growing
Not long cause I have 2 and there the same size
That is so big my one steppdad want one so much can we have it please?