When Is a Dog Fully Grown? (All Growth Phases)

Growth Speed

Small breeds are born considerably heavier relative to their final weight than large breeds. While small dogs multiply their birth weight by 25, large breeds can reach up to 100 times their birth weight. The fastest weight gain happens between the 3rd and 6th month of life.

After six months, small breeds have reached about 70% of their final weight, and very large breeds a little less. Although most dogs reach their maximum size at 1–2 years, body proportions and muscle mass can still change up to the age of 3 years.

The 7 Developmental Phases

Week 1–2: Neonatal Phase

The eyes and ear canals are still closed. The sense of smell is already developed. The puppy sleeps almost all day and nurses on its mother's milk. It can't yet regulate its own body temperature.

Week 3: Transitional Phase

The eyes and ears open. The puppy starts to move and to take in its surroundings and littermates. The first teeth break through.

Week 4–7: Imprinting Phase

Growing curiosity and interest in the surroundings. The future temperament becomes recognizable. Contact with people and littermates is especially important now.

Week 8–12: Socialization Phase

This phase shapes later social behavior. The puppy should get to know its environment without being overwhelmed. Dealing with the unfamiliar builds self-confidence.

Month 3–6: Ranking Phase

The puppy has to fit into the family. Clear, easy-to-understand rules help it find its place. Puppy training should be loving but consistent.

Month 7–12: Puberty Phase

The "rebellious phase": females come into heat for the first time, males feel the urge to reproduce. The dog tests boundaries and seems to forget what it has learned. Patience and consistency are key.

Month 12–30: Maturity Phase

The transition from puppy to adult dog. Physical growth is complete, but the dog keeps learning. A close bond and enough activity (physical and mental) are important in this phase.

Nutrition During the Growth Phase

The right nutrition is the most important factor for healthy growth. Three rules:

1. Weigh out the food. The recommendations on the package are guidelines. The amount actually needed varies. Better to feed a little less to avoid too-rapid growth. Count treats as part of the daily ration.

2. Avoid over- and undersupply. Special puppy food already contains the right nutrient balance. With raw feeding (BARF), consult an expert about ingredients and portion sizes. The two most common mistakes: overfeeding and too much calcium.

3. Control calcium intake. Too much calcium leads to disturbances in bone and cartilage remodeling (osteochondrosis). The body only regulates calcium absorption through vitamin D from the 5th month of life onward. Before that point, calcium is absorbed without limit.

Growing too fast between the 3rd and 6th month of life causes growth-related skeletal disorders. The circulatory system and muscles can't keep pace with skeletal development. Deformities of the front legs, lameness, and joint limitations appear in the following months.

How Big Will My Dog Get?

The breed is the clearest clue to the final size. With mixed breeds, the size of the parents, the puppy's paw size, and a DNA test when needed all help. Large paws point to a considerable final size.

The Fully Grown Dog

The best way to track growth progress is by measuring and weighing weekly. As soon as the size barely changes anymore, growth is complete. Depending on the breed, from the 10th month onward.

Keep an eye on weight even with a fully grown dog. Up to 18 months, the weight should sit at the lower end of the range. The ribs should always be easy to feel. Weigh regularly, even in adulthood.

You'll find every topic around dog ownership at Hundeo Pro. From training to nutrition to health: structured courses with video guides, training tracking, and personal help from real trainers when problems come up.