Guide
When Do American Bullies Stop Growing?
Height is done first, mass is done much later, and the months in between are where owners start to worry.
An American Bully stops gaining height between twelve and eighteen months, and stops broadening in width and mass somewhere from two to three years. The smaller classes wrap up sooner. A pocket is usually finished by twelve to fourteen months, while a heavy XL can still be widening across the chest at three.
Two separate clocks, running at different speeds
| What | When it finishes | How you know |
|---|---|---|
| Height at the withers | 12 to 18 months | Measurements stop changing over 6 to 8 weeks |
| Length of bone | 12 to 18 months | Growth plates close. Your vet can confirm |
| Chest width and depth | 2 to 3 years | The dog visibly broadens without gaining fat |
| Head and muzzle | 2 to 3 years | Last thing to finish. Males more than females |
| Muscle mass | Ongoing | Depends on condition and exercise, not on growth |
That gap between the two clocks is the whole reason a fourteen-month-old bully looks unfinished. It has hit its adult frame and has not yet built onto it, and there is nothing you can or should do to rush the second clock.
Why the growth plates outrank the calendar
Growth plates are bands of soft cartilage at the ends of the long bones, the sites where the bone lengthens. While they are open they are the weakest link in the whole skeleton, which is why a young dog can wreck a joint doing something an adult would brush off. They close as growth finishes, generally twelve to eighteen months in this breed, later in the heavy classes.
Until they close: no forced running, no repeated jumping down from a height, no long sessions on stairs. Once they close, a bully can take on normal adult exercise, inside whatever limits its build and the weather set, and for a short-muzzled dog in summer that limit is real.
Your vet can tell you whether the plates have closed. Worth asking at the twelve-month visit instead of guessing from the calendar.
Class by class
- Pocket: height done around 12 to 14 months, filled out by roughly 2 years.
- Standard and classic: height done around 14 to 16 months, filled out by 2 to 2.5 years.
- XL: height done around 16 to 18 months, and can still be broadening at 3.
The bigger the dog, the later it finishes. That holds across every breed, and it is exactly why exercise restrictions run longer on an XL than on a pocket.
The one mistake to steer clear of right now
Piling more food into a lanky yearling to hurry it along. You cannot feed a dog past the frame its genes drew for it, so the surplus turns into fat, and fat sitting on a skeleton that has only just finished forming is the precise load you spent eighteen months avoiding.
The dog fills out on its own schedule. Keep it lean, keep it fed properly, and at two or three it arrives looking like exactly what it was always going to be.
Month by month growth · Adult size by class · How much to feed
Ask about a particular puppy
What its parents measure, which class it is, and where it is likely to land. You will get the honest estimate.