How the puppy-weight model works
Merck Veterinary Manual (Feeding Practices in Small Animals) states that in the first 5 months
puppies gain an average of 2–4 g/day per kg of anticipated adult weight, with growth
beginning to plateau after about 6 months. Rearranging for age ≤ ~22 weeks with daily gain rate
r ∈ [2, 4] g/day/kg adult gives
adult_kg ≈ current_kg × 1000 / (age_days × r).
Faster assumed gain (4) yields a lower adult estimate; slower gain (2) yields a higher
estimate — hence a range, never a midpoint we pretend is exact.
What the output range means
The low and high adult weights bound Merck’s published early-growth band under the rearrangement above. Salt et al. 2017 size-category labels appear only as context for where that range sits among growth-standard charts — they are not a second formula competing with Merck.
When the model does not apply
- Past ~22 weeks we refuse a numeric projection (no invented late-age fractions).
- Failure to thrive, parasites, or underfeeding can invalidate the average-gain assumption.
- Giant breeds and litter outliers need clinical growth-chart monitoring, not a one-shot estimate.
- Weights or ages outside the form bounds are rejected.
When to consult a veterinarian
Prefer serial weigh-ins plotted on Salt/WALTHAM-style growth standards with your veterinarian. Seek care promptly for puppies that lose weight, plateaus early, or show GI illness — those patterns are clinical problems this estimator will not diagnose.
Puppy weight FAQ
- Why is the adult weight a range?
- Merck’s 2–4 g/day/kg anticipated adult weight band rearranges into a low–high adult estimate.
- What happens after 5 months?
- The tool refuses numeric projection past ~22 weeks and points to growth-standard monitoring instead.
- What are Salt 2017 bands for?
- Context labels from growth-standard size categories — not a second adult-weight equation.