Methodology
How accurate is this?
Short version: we predict a range for your puppy's adult weight, we tell you exactly how wide that range is, and it gets narrower every month as your puppy grows.
This page is the long version. Every number on it comes from the same veterinary growth data the prediction runs on, and we've written down the cases where it does worse just as carefully as the cases where it does well.
We predict exactly one thing: how much your dog is likely to weigh once fully grown, shown as a range with a middle estimate. We don't predict height, and we don't tell you whether any particular weight is good or bad for your dog — that's a conversation for your vet.
The numbers
In plain terms: if you first use the app when your puppy is 4 months old, our middle estimate is typically within about 12% of what they actually weigh as an adult. At 2 months it's about 15%. By a year, about 7%.
"Typically" means the median: half of predictions land closer than the figure below, and half land further away. It is the middle of the pack, not the best case, and it is not a guarantee for any individual dog.
| Puppy's age | Typical error | On a dog that grows to about 20 kg (44 lb) |
|---|---|---|
| 2 months | 14.8% | ±3.0 kg (±6.5 lb) |
| 3 months | 13.4% | ±2.7 kg (±5.9 lb) |
| 4 months | 12.1% | ±2.4 kg (±5.3 lb) |
| 6 months | 10.5% | ±2.1 kg (±4.6 lb) |
| 8 months | 9.0% | ±1.8 kg (±4.0 lb) |
| 12 months | 7.4% | ±1.5 kg (±3.3 lb) |
And the range narrows
The middle estimate is only half the story. Every prediction is shown as a range, and the range is the part that visibly tightens as your puppy grows. At 8 weeks, the top of the range is about 2.2 times the bottom of it. By 12 months, it's about 1.34 times.
In practice, a ×2.2 range on an eight-week-old puppy reads like "9 to 20 kg" (20 to 44 lb). That is a genuinely wide answer, and it is still a useful one — it rules a lot out. We would rather show you the width than invent a single confident number.
Where the data comes from
The growth model is built from 14.96 million anonymised veterinary weight records — real weigh-ins from real clinic visits, not survey answers, breeder estimates or breed-club averages.
The error figures above come from checking the model against roughly 394,000 dogs that were tracked from puppyhood all the way to adulthood. For each of those dogs we know both what the model would have predicted and what the dog actually grew into, which is the only way to put an honest number on how often we're wrong.
Source: Salt et al. 2017, PLOS ONE. Data used under CC BY 4.0.
What makes a prediction better or worse
Four things move the needle, and none of them are secret.
Sex matters more than people expect
Within the same breed, males and females typically differ by around 16% in adult weight. That's why the app asks — it's a single tap that shifts the estimate more than almost anything else you can tell us.
Breed helps most while your puppy is tiny
At eight weeks, knowing the breed is doing most of the work, because the puppy hasn't grown enough yet to reveal much on its own. By about a year, breed has stopped mattering — your dog's own weigh-ins already say everything the breed would have. The app detects the breed from the photo and lets you correct it, which counts for most in those early months.
Mixed breeds work from about 4 months
When there's no clean breed label to lean on, the prediction has to lean on the growth curve itself. From roughly 4 months, a mixed-breed puppy's own measurements carry enough signal to predict from properly. Before then, treat the number as a wide first guess — because that's what it is.
Giant and toy breeds get wider ranges
At both ends of the dog world there is simply more variation in what an adult ends up weighing. If your puppy is a giant or a toy breed, expect a wider band, especially in the first few months. We'd rather widen the range than pretend it's narrow.
What we don't claim
These are the limits of the thing. We'd rather you heard them from us.
Monthly weigh-ins don't magically make us right
Weighing your puppy every month doesn't improve the model underneath. What it does is update the estimate with new evidence and narrow the range around it. Those are two different things, and the second one is the useful one.
Adult size isn't settled at birth
What a dog eats and how it lives change where it ends up. So what we actually predict is where a typical dog on your puppy's current trajectory tends to land. If the trajectory changes, the prediction should change with it — which is exactly what the monthly weigh-ins are for.
We don't tell you whether anything is wrong
The app can show you that your puppy is tracking above or below the typical curve for its size. It can't tell you what that means, and it doesn't try. If a weigh-in surprises you, ask your vet — reading that signal is their job, not an app's.
The grown-up portrait is a prediction, not a photograph
The adult portrait the app produces is AI-generated from your puppy's photo and the predicted adult size. It is an illustration of what a dog like yours tends to grow into — not a photo of your dog, and not a promise about their markings, coat or face. It carries an AI-generated label everywhere it appears, share cards included.
Measured, not assumed
About "double the weight at 4 months"
It's the rule everyone repeats, and for plenty of medium-sized dogs it isn't bad. We didn't want to argue with it, so we measured it against the same veterinary records the model is built on.
On giant breeds, the rule under-predicts adult weight by about 24%. That's a serious miss, and it's a miss in the direction that matters most: it tells the owner of a very large dog to expect a much smaller one.
The rule also knows nothing about your puppy's sex, and it hands you one number instead of a range — so it can never tell you how sure it is. That last part is the whole point of this page.
Everything on this page and in the app is an estimate, produced for information and for fun. It is not veterinary advice, it is not a substitute for weighing your dog, and it says nothing about your individual puppy's health. Talk to your vet about growth, food, and anything that worries you.
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