Kitten Growth Calculator
How big will your kitten get? Enter its age and what it weighs today and get a predicted adult weight, plus the weight to expect at every weigh-in until it is fully grown. No breed needed — it works for mixed-breed kittens too.
Not sure? Leave it on “Most cats” — it fits mixed-breed kittens.
Predictions come from typical growth curves for cats, not from your individual kitten's genetics. Neutering, diet and the size of both parents all move the final number — ask your vet if the answer looks far off what you expected.
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How the prediction is made
Kittens grow fast, but they grow on a predictable curve. A typical kitten is about a third of its adult weight at three months and around 60% at six months. Big, slow-maturing breeds like the Maine Coon are only a quarter of the way at three months, because they keep growing for years rather than months.
The calculator takes the share of adult weight a kitten has typically reached at its age, then divides:
adult weight = current weight ÷ share of adult weight reached
A three-month-old mixed-breed kitten at 1.3 kg is about 33% grown, so it projects to roughly 3.9 kg. A three-month-old Maine Coon at 1.6 kg is only 25% grown, so it projects to about 6.4 kg.
The shares come from the same growth curves used to build the cat breed weight charts on this site, so a prediction here will never contradict the chart for your cat's breed.
How much of its adult weight a kitten has reached
The table the calculator runs on. Read across to see how much growing is left at each age.
| Type of cat | 8 weeks | 3 months | 6 months | 9 months | 12 months | Fully grown |
|---|---|---|---|---|---|---|
| Most cats | 20% | 33% | 60% | 80% | 93% | 12–18 months |
| Large, slow-maturing breed | 15% | 25% | 45% | 60% | 75% | 3–5 years |
These are typical figures, not a breed standard. Individual kittens run ahead of or behind the curve and still finish in a normal place.
Is your kitten growing at the right pace? Ask PetNoter AI.
PetNoter AI reads your cat's own weight log, so it can tell you whether a change is normal for their age and breed, and when it is worth a vet visit.
Free to download · AI with PetNoter Pro · How PetNoter AI works
Luna
PetNoter AI
Luna has put on weight this year. Should I worry?
PetNoter AI's suggestion
Monitor at home
Keep an eye on it and contact a vet if it gets worse.
Luna's weight log shows a steady rise since March. A slow gain like this is common in indoor cats, so keep logging her weigh-ins and ask your vet to check her body condition at her next visit.
Not a vet. In an emergency, contact a vet right away.
You know the numbers. Now watch the trend.
A single weigh-in tells you very little — a chart of the last six months tells you everything. PetNoter keeps your kitten's weight history in one place, free.
- Log a weigh-in in seconds and see the trend line
- Reminders for weigh-ins, vaccinations and vet visits
- Vet records, prescriptions and photos stored per pet
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How much to trust the number
- Under 12 weeks: broad. A kitten has reached a fifth to a third of its adult weight, so the curve being slightly off, or the kitten having just eaten, moves the answer noticeably.
- Four to six months: the sweet spot. Enough growth has happened for the prediction to be a useful guide.
- Nine months and up: close for most cats. Slow- maturing breeds still have a lot of filling out to do.
- Chubby kittens read high. The calculator cannot tell fat from frame, so an overweight kitten projects to a larger adult than it will really be.
Use the prediction as a plan to check against, not a target to feed towards. Weigh your kitten every week or two while it is growing and watch whether it follows its own curve. A kitten that suddenly stops gaining, or loses weight, is worth a vet's attention.
Frequently Asked Questions
How does the kitten growth calculator work?
It works backwards from a growth curve. Kittens reach a predictable share of their adult weight at each age — a typical kitten is around a third grown at three months and about 60% at six months — so dividing the current weight by that share gives the adult weight. Enter your kitten's age and what it weighs today, and the calculator returns a predicted adult range plus the weight to expect at every age until it is fully grown.
How big will my kitten get?
Most mixed-breed domestic cats finish between about 3 and 6 kg (7–13 lbs), with males usually heavier than females. Large breeds such as the Maine Coon and Ragdoll can reach 8–9 kg (18–20 lbs). For a kitten of unknown breed, its own current weight is the best signal — enter the age and weight and the calculator projects from there.
How accurate is a kitten weight prediction?
Accuracy improves with age. From about four to six months the prediction is a useful guide. At eight to ten weeks it is rougher, because the calculation divides by a small number and multiplies any error along with it. That is why the calculator returns a range rather than a single figure, and why the range narrows as your kitten grows.
When do kittens stop growing?
Most cats reach their adult weight between 12 and 18 months. Large, slow-maturing breeds keep filling out for much longer — a Maine Coon or Norwegian Forest Cat can still be gaining at three to five years, and a Ragdoll until three or four.
Does the calculator work for mixed-breed kittens?
Yes. Leave the breed empty and keep the type on "Most cats", which follows the growth curve that fits mixed-breed domestic cats. If you know your kitten has Maine Coon or Ragdoll in it and is clearly large for its age, the slow-maturing option may fit better.
Why won't it predict for a kitten under eight weeks?
Because the answer would not be worth having. A kitten under eight weeks is usually still with its mother, its weight moves with the last feed, and it has reached well under a fifth of its adult weight — so a small weighing error becomes a large error in the prediction. Weigh again at eight weeks.
Does neutering change how big a kitten gets?
Neutering lowers a cat's energy needs, so weight gain afterwards is common if portions stay the same. That gain is fat rather than growth, and no growth curve can predict it. Talk to your vet about adjusting food after the operation.
Related tools
Check whether your cat is a healthy weight for its breed →
Convert your cat's age to human years →
Track your kitten's weight in the free PetNoter app
4.5 · Free · Android & iOS