When do American Cocker Spaniels stop growing?

American Cocker Spaniels typically stop growing in height by about nine months of age, though some may continue to fill out and build muscle until they’re around 12 months. 

By the time they’re nine to 10 months old, most American Cockers are ready to transition from puppy to adult food, as they’ve developed the structure and metabolism of an adult dog. This is also a great time to ensure they’re getting the right balance of nutrients for maintaining a healthy weight and supporting their joints, which can help prevent common issues as they age.