How big will my puppy get?
Enter your puppy's age and current weight. You get an estimated adult weight, the range around it, and a growth chart you can print and fill in as they grow.
How this is calculated
Puppies of different adult sizes grow on very different timetables, so the method is: work out roughly what fraction of its adult weight a puppy of this size category has reached at this age, then divide.
Adult weight ≈ weight now ÷ fraction of adult weight reached
The anchor points this is built from
These are the commonly published figures for each size category. Ages in between are filled in by straight-line interpolation — there is no hidden model, and you can check any number in the table yourself.
| Size category | Published anchor points | Fully grown |
|---|---|---|
| Toy | 25% at 6 weeks · 50% at 13 weeks | ~8–9 months |
| Small | 25% at 6 weeks · 50% at 15 weeks · 90% at 6 months | ~8–12 months |
| Medium | 40% at 14 weeks · 50% at 19 weeks · 99% at 9–10 months | ~12 months |
| Large | ~62% at 6 months · 75% at 7 months | ~12–15 months |
| Giant | 22% at 3 months · 53% at 6 months · 83% at 12 months | ~18–24 months |
Where the range comes from
The range is not a made-up percentage. It is what you get if your puppy is actually tracking the size category below or above the one you picked — which is the most common reason these estimates go wrong. If the range looks uncomfortably wide, that width is real information, not a failure of the tool.
One honest caveat about large breeds: published methods genuinely disagree. The familiar “double the weight at six months” rule implies a large puppy is 50% grown at six months; growth charts put it nearer 75%. This tool sits between them, which is why large-breed estimates carry more uncertainty than small-breed ones.
What this cannot do
This is a size estimate, not a health assessment and not veterinary advice. For clinical monitoring — is my puppy growing at a healthy rate, not just to a predictable size — ask your vet about the WALTHAM puppy growth charts, which use centile curves built from around 50,000 healthy dogs and validated against six million veterinary records (Salt et al., 2017, PLOS ONE).
Questions people actually ask
How accurate is this?
It is an estimate, and it should be treated as one. Two puppies from the same litter can finish 20% apart. The estimate is most reliable for small and medium dogs and least reliable for large and giant breeds, where published methods disagree with each other — one common rule says a large puppy is half its adult weight at six months, growth charts say closer to three quarters. That is why this tool shows a range rather than a single confident number.
What is the most accurate way to track my puppy's growth?
Ask your vet about the WALTHAM puppy growth charts. They are the clinical standard, built from around 50,000 healthy dogs and validated against six million veterinary records (Salt et al., 2017, PLOS ONE). They use centile curves in the same way human infant growth charts do, and your vet can plot your puppy on the right one. A free web tool cannot replace that — but it can tell you roughly what to expect and when to ask questions.
My puppy is a mixed breed. Which size category do I choose?
Pick the category that matches what you expect the adult dog to weigh, not what the puppy weighs now. If you genuinely do not know, run it twice with the two most likely categories — the gap between the answers is the honest size of your uncertainty.
Why does breed size category change the answer so much?
Because small dogs finish growing much earlier than big ones. A toy breed is about half its adult weight at three months and done by eight or nine months. A giant breed is only about half way there at six months and may keep filling out until two years old. The same puppy weight at the same age means very different things in those two cases.
Should I use this to decide how much to feed?
No. Feeding amounts depend on your puppy's body condition, activity, and the specific food, and getting it wrong matters — overfeeding a large-breed puppy is linked to joint problems. Use the feeding guide on your food and your vet's assessment of body condition. This tool estimates size, nothing more.
Does neutering change adult size?
It can affect the timing of growth: removing sex hormones delays the closing of growth plates, so dogs neutered early may end up slightly taller and leaner in build. This is an area where the evidence is still developing and it varies by breed. It is a conversation to have with your vet, not something this calculator models.
Last checked: 2026-08-09