Guide
When Do American Bullies Stop Growing?
Height finishes first, mass finishes much later, and the gap between the two is where most owners get worried.
An American Bully stops growing in height between twelve and eighteen months, and stops filling out in width and mass somewhere between two and three years. Smaller classes finish earlier: a pocket is usually done by twelve to fourteen months, where a heavy XL can still be broadening at three.
Two different things finish at two different times
| 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 |
This is why a fourteen-month-old bully looks unfinished. It has reached its adult frame and hasn’t yet built onto it, and there’s nothing you can or should do to hurry that.
Why the growth plates matter more than the calendar
Growth plates are soft cartilage at the ends of the long bones where lengthening happens. While they’re open they’re the weakest part of the skeleton, which is why a young dog can damage a joint doing something an adult would shrug off. They close as growth finishes, generally between twelve and eighteen months in this breed and later in the heavier classes.
Until they close: no forced running, no repeated jumping down from height, no long stair sessions. After they close, a bully can do normal adult exercise, within the limits its build and the weather allow, which for a short-muzzled dog in summer is a real limit.
Your vet can tell you whether they have closed. It’s worth asking at the twelve-month visit rather than guessing.
Class by class
- Pocket: height done around 12 to 14 months, filled out by about 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.
Bigger dogs finish later. That’s true across all breeds and it’s the reason exercise restrictions run longer for an XL than for a pocket.
The mistake to avoid at this stage
Feeding a lanky yearling more in the hope of filling it out. You can’t feed a dog past its genetic frame, so the surplus becomes fat, and fat on a skeleton that has only just finished forming is the exact load you spent eighteen months avoiding.
The dog will fill out on its own. Keep it lean, keep it fed properly, and it arrives at two or three looking like what it was always going to look like.
Month by month growth · Adult size by class · How much to feed
Ask about a particular puppy
What its parents measure, what class it is, and where it’s likely to finish. I’ll give you the honest estimate.