When Do Dogs Stop Growing? A Guide by Breed Size

The answer to when do dogs stop growing varies significantly based on the breed’s size category. When are dogs fully grown in physical terms involves both skeletal development and muscle filling, which happen at different rates. What age do dogs stop growing in terms of bone plates closing is the most important biological milestone. When are dogs full grown in terms of body weight, head shape, and chest depth can lag behind skeletal maturity by several months. Understanding when do dogs reach full size helps owners make better decisions about nutrition, exercise, spay or neuter timing, and joint health supplementation.

We’ve organized the key information by breed size category so you can find the most relevant guidance for your specific dog.

Growth Timelines by Breed Size

Small Breeds: Rapid Maturity

Small breed dogs, generally under 20 pounds, mature earliest. When do dogs stop growing for small breeds is typically between 9 and 12 months of age. Their growth plates, the cartilaginous areas at the ends of long bones that allow bone lengthening, close earlier than those of larger breeds. Toy breeds like Chihuahuas and Yorkshire Terriers may reach near-full adult size by 6 to 8 months. While when are dogs fully grown physically comes early for small breeds, their muscle development and body composition continue filling out until 12 to 14 months in many cases.

Medium Breeds: Moderate Timeline

Medium breeds, typically between 20 and 50 pounds, reach skeletal maturity between 12 and 15 months. Breeds like Beagles, Cocker Spaniels, and Border Collies fall into this category. What age do dogs stop growing for a medium breed is usually stated as 12 months, but visible body changes, particularly filling of the chest and development of the hindquarters, often continue until 14 to 16 months. Dogs in this size range are considered when are dogs full grown for feeding purposes by most commercial pet food brands at 12 months, prompting a transition to adult formulas.

Large and Giant Breeds: Extended Development

Large breeds, defined as 50 to 90 pounds, typically stop skeletal growing between 15 and 18 months. Giant breeds, including Great Danes, Saint Bernards, and Mastiffs, may not reach full skeletal maturity until 18 to 24 months. When do dogs reach full size for a Great Dane or Newfoundland could be close to 2 years by strict skeletal criteria. This extended growth window has important implications for feeding, as large breed puppy formulas are designed to support slower, controlled bone growth that reduces the risk of developmental orthopedic disease. Transitioning to adult food too early can disrupt this balance.

Why Growth Completion Matters for Health Decisions

Spay and Neuter Timing

Emerging research has shifted veterinary thinking on spay and neuter timing, particularly for large breed dogs. Sex hormones play a role in growth plate closure, and early spay or neuter, before growth plates close, can result in longer leg bones and altered body proportions. For large and giant breeds, many veterinarians now recommend delaying sterilization until after when are dogs fully grown by skeletal criteria. For small breeds with earlier maturity, the timing question is less consequential. This is a nuanced conversation best had with your specific veterinarian based on your dog’s breed and individual risk factors.

Exercise and Joint Protection During Growth

Before growth plates close, high-impact repetitive exercise such as long-distance running, jumping from significant height, or intense agility training carries a higher risk of growth plate injury. The growth plate is structurally weaker than mature bone during active development. For large breed puppies where when do dogs reach full size extends well past a year, this means moderating high-impact activities until 18 months or later. Leash walks and play on natural surfaces are generally appropriate throughout puppyhood; structured endurance exercise should wait until skeletal maturity is confirmed.

Puppy Food Transition Timing

Puppy formulas are calorie-dense and formulated with higher protein and fat levels to support growth. Staying on puppy food past skeletal maturity contributes to excess weight gain in small and medium breed dogs. What age do dogs stop growing is also the benchmark for transitioning to an adult maintenance formula. For small breeds, transition at 12 months. For large breeds, transition around 15 to 18 months. Giant breeds may benefit from large breed puppy formulas all the way to 18 to 24 months. Your vet can help confirm readiness based on body condition scoring.

Pro tips recap: Track your dog’s breed size category and use it as the primary guide for growth completion timing rather than age alone. Schedule a body condition assessment with your veterinarian around the expected maturity age to confirm appropriate weight and proportions. Delay high-impact exercise and discuss spay or neuter timing with your vet if you have a large or giant breed dog.