When should you switch a kitten to adult cat food?

Most cats are ready for adult food at around twelve months, and large slow- maturing breeds often stay on growth food until eighteen months or more. The calendar is a guide; your vet's read on your particular cat is the decision.

The signal is that growth has essentially stopped. A cat that has reached its adult frame does not need the extra calorie density that kitten food is built around, and continuing to feed it is how a lean young cat quietly becomes a heavy one.

Rough timing by type of cat

Nothing in that table beats a hands-on assessment. If your vet says your fourteen-month-old Maine Coon is still filling out, they are right and the calendar is not.

How to tell growth has finished

• Weight has been steady across two or three weigh-ins rather than climbing.
• The cat looks proportioned rather than leggy and adolescent.
• Your vet's body condition score is where they want it.

Weight that is still climbing steadily at twelve months usually means growth is continuing — or that the portions are too big. Those two look identical on a scale and different in the hands, which is the whole reason vets score body condition by feel rather than by number.

How to make the change

Go gradually. A cat's gut microbiome adjusts to a diet, and a sudden swap is a reliable way to produce a week of loose stool.

Mix the two together in the same bowl rather than offering them side by side — a cat given a choice will simply eat the familiar one and leave the rest. If stool goes soft at any step, drop back to the previous ratio for a few days before moving on again.

The portion changes too, not just the bag

This is the part people miss. Adult food is less calorie-dense, so the same scoop is a smaller amount of energy — but adult cats also need far fewer calories per pound than growing kittens do. The net result is that the portion usually needs recalculating from scratch rather than carried across.

Start from the new food's own feeding guide for your cat's weight, then adjust by body condition over the following month. Our food portion calculator gives you a starting figure, and the same logic that governed kitten portions still applies: the bag is a starting point, the cat is the evidence.

Meal frequency can drop too. Most adult cats do well on two meals a day, and many households keep a third small one because it suits their schedule.

If the transition isn't going smoothly

Soft stool for the first day or two after a step up in the new food's ratio is common and usually settles on its own. If it hasn't improved after three days at a given ratio, drop back to the previous step and hold there a few extra days before trying again — there's no harm in stretching the ten-day plan out to two or three weeks for a sensitive stomach. What's not a normal transition hiccup: repeated vomiting, diarrhea that doesn't let up, or a cat that stops eating either food. Those warrant a call to your vet rather than another few days of waiting it out, since they may mean the new food itself doesn't agree with your cat rather than just needing a slower ramp.

For a cat that's a slow, picky eater

A cat that already eats slowly or picks at food can make the mixed-bowl method harder to judge, since it's not always obvious whether they're eating the new food or leaving it in the bowl. Weigh the cat weekly during the transition rather than relying on how much looks eaten, and don't assume a picky eater "isn't ready" for adult food — a slow eater usually just needs a longer transition window and smaller, more frequent portions of the mixed food rather than a different approach altogether.

In a multi-cat household with different ages

Feeding a kitten still on growth food alongside adult cats already switched takes some separation, since a kitten who's ready to switch but still shares a bowl with a growing littermate on kitten food will simply eat whichever is in front of them. Feed by age group in separate spots or at separate times until every cat in the house is confirmed to be on the food appropriate for their own stage — a shared bowl makes it impossible to know who actually ate what, and impossible to catch a kitten quietly falling behind or a switched adult quietly overeating growth food.

The two mistakes worth avoiding

Switching early to save money. Growth food is more expensive, and a ten-month-old kitten still doing real growing is the wrong place to economize. The gap in cost over two months is small next to the value of getting the last stretch of development right.

Switching late and not noticing. The opposite error is more common and harder to see, because nothing appears to go wrong. Weight creeps, the cat stays cheerful, and eighteen months later a vet mentions it. If you are unsure whether it is time, ask at the next appointment — a switch decision is a thirty-second conversation.

What to do next

Book the twelve-month check if you have not already, ask your vet directly whether your cat is done growing, and start the ten-day transition once they say yes. Then weigh the cat once a month for the next few months so you catch any drift early, while it is still a portion adjustment rather than a weight-loss plan. Our cat food guide covers the adult foods we recommend.