When Do American Bullies Stop Growing — The Full Timeline
When do American Bullies stop growing has two answers, because height and mass finish at very different times. Height is essentially done by twelve months. Width, chest and head keep developing until two, and until three in the largest class. Knowing which is which tells you when it is safe to exercise the dog properly. See the growth chart.
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Height Stops Before Weight
Long bones grow from soft cartilage plates near each end. Once those plates close, the dog cannot get any taller. That is the hard stop, and it comes early relative to how the dog looks.
Everything after is filling out: muscle, chest depth, shoulder width, head size. That is why a twelve-month-old bully looks lanky compared to what it will become, and why owners worry unnecessarily.
Growth Timeline by Class
| Class | Height complete | Weight complete | Fully mature |
|---|---|---|---|
| Micro | ~10 months | ~18 months | 18–24 months |
| ~11 months | ~20 months | ~2 years | |
| Classic | ~12 months | ~22 months | ~2 years |
| Standard | ~12 months | ~22 months | ~2 years |
| XL | 12–14 months | 2–2.5 years | 2–2.5 years |
| XXL | 14–16 months | 2.5–3 years | 2.5–3 years |
Larger dogs take longer at every stage. An XXL is still visibly changing at two and a half years old.
What Happens When
| Age | What is happening |
|---|---|
| 0–4 months | Fastest growth of the whole life. Height and length increase rapidly |
| 4–8 months | Growth continues but slows. The lanky adolescent phase |
| 8–12 months | Height nearly final. Chest begins to deepen |
| 12–18 months | Growth plates close. Muscle and width develop |
| 18–24 months | Head broadens, chest fills, coat thickens |
| 2–3 years | Final filling out: XL and XXL only |
Why Growth Plate Closure Matters
This is the practical reason to care about the timeline. Until the plates close, the joints are soft and vulnerable, and two decisions depend on it:
Exercise
Avoid forced running, repetitive jumping and long sustained walks on hard ground until the plates close — 12–18 months, later for XL and XXL. Damage done to open growth plates causes permanent deformity. Free play at the puppy's own pace is fine; a five-mile run beside a bicycle is not.
Neutering timing
Sex hormones are part of what signals the growth plates to close. Neutering early delays closure, producing a taller, lankier dog with altered joint angles. And in large breeds this is associated with a higher rate of joint problems and cruciate injury.
For an American Bully, most vets now recommend waiting until growth is complete: roughly 12–18 months depending on class, later for XL and XXL. Take your own vet's advice, but ask the question rather than defaulting to six months.
Signs Your Bully Has Finished Growing
- Height unchanged for three months or more
- Weight stable at a consistent feeding level
- Chest fully dropped to elbow level
- Head broad and proportionate rather than narrow
- Adult coat texture settled
- Movement noticeably more coordinated, the adolescent clumsiness gone
Common Worries
"My 8-month-old looks skinny and leggy." Normal. This is the adolescent phase and it resolves. Do not add food to fix it, that adds fat, not frame.
"He stopped growing at 10 months." Height likely has finished. Width has not. Expect substantial change over the next twelve months.
"She's smaller than the chart." Charts are ranges. If the dog is lean, energetic and steadily progressing, it is likely fine. Genetics set the ceiling.
See the weight chart for adult targets and the feeding guide for portions during growth.
When Do They Stop Growing? — Frequently Asked Questions
At what age do American Bullies stop growing?
Height finishes around 12 months for most classes, 14–16 for XXL. Weight and width continue to about two years, and up to three for XXL. The two are separate processes.
When do American Bully growth plates close?
Between roughly 12 and 18 months, later in XL and XXL. Until then, avoid forced running and repetitive jumping. Damage to open growth plates causes permanent deformity.
When should I neuter my American Bully?
Most vets now recommend waiting until growth is complete — 12–18 months depending on class, later for XL and XXL. Early neutering delays growth plate closure and is associated with higher joint injury rates in large breeds. Ask your own vet.
My American Bully looks skinny at 8 months, is that normal?
Yes, very. Height comes before width and the adolescent phase looks lanky in every large breed. Do not increase food to compensate; that adds fat, not frame.
Text Us at Any Age
Send us a photo at eight months when your bully looks lanky and we will tell you honestly whether it is on track. We stay available for the life of the dog. That is the point of buying from a breeder.
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