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Your puppy's likely adult weight, worked out from the size class growth curves used on our breed profiles.
Puppies do not grow at one steady speed, and size changes everything. A toy puppy is most of the way to adult weight before its first birthday, while a giant breed puppy is still adding weight well into its second year. This calculator uses the growth curves by size class published by the Waltham Petcare Science Institute, the same curves behind the growth tables on our breed profiles. Each age on the curve carries a typical fraction of adult weight for that size class, so dividing your puppy's current weight by that fraction gives a central estimate of adult weight. We show it as a range, 10 percent either side, because that is the honest shape of the answer.
Individual puppies vary. A puppy can sit above or below the curve for weeks and still finish at a perfectly normal adult weight, and mixed breed puppies follow the size class of the adult they are heading toward, which is not always obvious at eight weeks. Steady growth matters more than hitting any single number, and your vet's growth checks come first: if a puppy is gaining too fast, too slowly, or losing weight, that is a conversation for the clinic, not a calculator. For the full picture by breed, see the growth tables on our breed profiles, which apply these same curves to each breed's standard adult weight range.
Every figure on this page is an estimate with its method shown. Read how we check facts, formulas and ranges on our methodology page.
Last updated: November 2026
It is a guide, not a promise. The estimate comes from size class growth curves, so it fits a typical puppy of that size class well, but individual puppies vary with genetics, sex, neutering and feeding. That is why the result is shown as a range 10 percent either side of the central estimate. Predictions get steadier as the puppy gets older, because a nine month reading rests on a much larger fraction of adult weight than an eight week reading.
It depends on size. Toy and small breeds are close to full size at about 12 months, medium breeds finish at about 18 months, and large and giant breeds keep filling out until about 24 months. Height usually arrives before the final muscle and chest width, so a young dog can look finished while the scale is still moving.