Predict your puppy's adult weight and track growth milestones
Puppy weight prediction uses growth curves that track what percentage of adult size puppies typically reach at each age. The formula varies by breed size because small and large breeds grow at very different rates.
A common rule of thumb: small/medium breeds are ~50% of adult weight at 16 weeks; large breeds are ~50% at 20 weeks; giant breeds are ~50% at 24–28 weeks. So: current weight ÷ percentage at current age × 100 = estimated adult weight.
The most reliable formula for small and medium breeds: weight at 16 weeks × 2 = approximate adult weight. For large breeds: weight at 20 weeks ÷ 0.5 (i.e., × 2). For giant breeds: weight at 24 weeks ÷ 0.45. For mixed breeds, average the expected weights of both parents as a baseline. If you have the puppy's weight at multiple ages, growth curves (available from your vet) give the most accurate prediction.
This varies significantly by size: Toy and small breeds stop growing at 8–12 months. Medium breeds at 12–15 months. Large breeds at 15–18 months. Giant breeds continue growing until 18–24 months — a Great Dane or Saint Bernard isn't fully grown until nearly two years old. Mental and emotional maturity often lags behind physical maturity by 6–12 months more.
If your puppy will weigh more than 25 kg (55 lbs) as an adult, large-breed puppy food is strongly recommended. These formulas contain controlled calcium and phosphorus (around 1.1% calcium vs 1.4–1.6% in regular puppy foods) and lower calorie density. This slows growth to a biologically appropriate rate, reducing the risk of osteochondrosis (OCD), elbow dysplasia, and hip dysplasia — all of which are worsened by rapid, calcium-heavy growth.
Healthy puppies roughly double their birth weight in the first 7–10 days. After that, small breeds gain ~5–10 g/day in early weeks; large breeds gain 70–90 g/day. Puppies should always be gaining weight, not losing it (except in the first 24–48 hours of life). A puppy that fails to gain weight for more than 2–3 days needs vet attention. Monthly weigh-ins help track growth and catch problems early.
Genetics are the biggest factor — the size of the parents predicts adult size more reliably than any formula. Other factors: sex (males typically weigh 10–20% more than females of the same breed); spay/neuter timing (early neutering delays growth plate closure, potentially adding 1–2 cm of height); nutrition (over-nutrition in large breeds causes abnormal bone development; under-nutrition stunts growth); and health (intestinal parasites, parvovirus, and chronic illness during puppyhood can affect adult size).