Puppy Growth Glossary: Growth Plates, Maturity & Size Categories

July 14, 2026

Why This Vocabulary Matters

Predicting adult dog weight relies on a handful of specific growth concepts, and knowing them helps put a result from the puppy weight calculator in proper context.

Growth Plates

Growth plates (epiphyseal plates) are areas of developing cartilage near the ends of a puppy’s long bones where new bone growth occurs. They remain open — allowing continued growth — until a dog reaches skeletal maturity, at which point they close (fuse). Larger breeds keep their growth plates open longer than smaller breeds, which is a major reason giant breeds continue gaining size well past a year old.

Size Category

A size category — toy/small, medium, large, or giant — groups breeds (or estimated adult sizes for mixed-breed puppies) by their typical adult weight range. Each category follows a meaningfully different growth curve, which is why the puppy weight calculator asks for size category rather than applying one universal growth curve to every puppy.

Percent of Adult Weight

Percent of adult weight is the estimated share of eventual adult body weight a puppy has reached at a given age, based on typical growth curves for its size category. It’s the core figure the puppy weight prediction formula divides current weight by.

Skeletal Maturity

Skeletal maturity is the point at which a dog’s growth plates have closed and bone growth has stopped. According to VCA Animal Hospitals, small and medium breeds typically reach adulthood by 10–12 months, while larger breeds can take up to 18–24 months — skeletal maturity specifically refers to bone growth stopping, which is distinct from filling out in muscle and body condition, which can continue somewhat after bones stop lengthening.

Rapid Growth Phase

The rapid growth phase is the period of a puppy’s life with the fastest weight and size gain, typically the first several months of life. According to VCA Animal Hospitals, the end of this phase — not full adult maturity — is often what people mean when they say a puppy has “stopped growing,” even though smaller size or condition changes can continue afterward.

Developmental Orthopedic Disease

Developmental orthopedic disease is a category of skeletal growth disorders — including hip dysplasia and hypertrophic osteodystrophy — more common in large and giant breed puppies, often linked to overnutrition, excess calcium intake, and rapid growth rate during the developmental window. See large breed growth and nutrition risks for how this connects to feeding decisions.

Littermate Variation

Littermate variation refers to the normal range in adult size among puppies from the same litter, even with identical genetics on the parents’ side and identical nutrition — a reminder that any weight prediction, including this calculator’s, is a statistical estimate rather than a guarantee for an individual puppy.

Putting the Terms Together

Once you know how size category, growth plates, and skeletal maturity relate to each other, a prediction from the puppy weight calculator tells a fuller story than just a single number. See common puppy weight prediction mistakes for the errors that most often affect prediction accuracy.