How the calculator works
A plain-English explanation of the method, its assumptions and its limits.
1. Size groups grow at different speeds
Small dogs finish growing much earlier than big ones. We group breeds into five size classes, each with its own growth curve: the share of adult weight a typical puppy has reached at each age.
| Size group | 8 wk | 12 wk | 16 wk | 26 wk | 52 wk | Full size |
|---|---|---|---|---|---|---|
| Toy (under 12 lb) | 28% | 47% | 61% | 84% | 100% | ~12 mo |
| Small (12–25 lb) | 25% | 45% | 58% | 80% | 100% | ~12 mo |
| Medium (25–50 lb) | 20% | 37% | 50% | 73% | 98% | ~15 mo |
| Large (50–100 lb) | 17% | 32% | 45% | 66% | 93% | ~18 mo |
| Giant (100 lb+) | 12% | 25% | 35% | 55% | 85% | ~24 mo |
These curves are approximations built from commonly published breed growth charts and rules of thumb. They are not a peer-reviewed veterinary model, and we will refine them as we compare predictions with real growth records.
2. From today’s weight to adult weight
If a large-breed puppy is 12 weeks old, the curve says it has probably reached about 32% of its adult weight. A 22 lb puppy at that point would end up around 22 ÷ 0.32 ≈ 69 lb. Between the listed ages we interpolate in a straight line.
3. Why we show a range
Young puppies are harder to predict, so the range is wider early on and narrows as your puppy grows: roughly ±20% at 8 weeks for a large breed, down to about ±10% near adulthood.
4. Breed and parent checks
For pure breeds we compare the estimate with the typical adult range for that breed and sex, and flag results that are far outside it. For mixed breeds, the parents’ adult weights choose the size group and act as the reference range.
Limits
- Genetics, diet, illness, activity and neutering timing all change growth.
- Mixed breeds and designer crosses vary the most, even within a litter.
- Predictions before 6 weeks and after 2 years are not shown.
- This is not a diagnostic tool. If you are worried about your puppy’s growth, see your vet.