When to Switch From Kitten Food to Adult Cat Food

Quick answer The AAFP/AAHA life stages end the kitten stage at about one year, so many cats move to adult food around 12 months; ask your vet for your cat. The calorie target drops sharply: a 3.5 kg kitten needs about 448 kcal at 2.5 times resting energy, but a neutered adult of that weight needs about 215 kcal at 1.2 times.

At some point the bag of kitten food starts to look like it belongs to a smaller cat. The kitten is long and lean, has stopped gaining weight so fast and is behaving more like an adult. The question is when to change, and the answer has two parts: the timing, which your vet confirms, and the amount, which you can work out yourself. The amount is the part owners get wrong, because the calorie target falls sharply at the switch.

What the guidelines say about timing

The AAFP/AAHA Feline Life Stage Guidelines (2021) define the kitten stage as the first year of life, followed by young adult (1 to 6 years), mature adult (7 to 10) and senior (over 10). Growth foods are built for the first stage, and an adult maintenance food suits the later ones. Many vets move kittens to adult food at around 12 months, but some cats, particularly larger ones, keep filling out later, and some have reasons to change earlier or later. Ask your vet at the 12-month check, with a recent weight and a note of the food and amount.

Our guide to cat life stages places this change in the whole timeline.

The calorie drop

The calculators use resting energy, RER = 70 × weight in kg ^ 0.75, multiplied by a factor. A kitten uses 2.5. A neutered adult uses 1.2, an intact adult 1.4 and an inactive or weight-prone adult 1.0. For the same body weight, the change at the switch is large.

Weight	RER	Kitten (2.5×)	Neutered adult (1.2×)	Drop at the switch
2 kg	118	294	141	52%
3 kg	160	399	191	52%
3.5 kg	179	448	215	52%
4 kg	198	495	238	52%

The drop is the same percentage at every weight because both numbers share the same resting energy. A kitten at 3.5 kg on 448 kcal has to come down to about 215 kcal as a neutered adult of the same weight: less than half.

Cats do gain weight as they go from kitten to adult, so in practice the adult amount is calculated at the new, heavier weight. A kitten of 3.5 kg at 10 months might be 4 kg at 14 months, and the adult target at 4 kg is 238 kcal.

A worked example in grams

A kitten weighs 3.5 kg at 11 months and eats 448 kcal of a 4,000 kcal/kg kitten food: 112 g a day. At 12 months, the vet agrees to switch to an adult food of 3,800 kcal/kg. The cat is neutered and weighs 3.6 kg.

Resting energy at 3.6 kg: 70 × 3.6 ^ 0.75 = 183 kcal.
Neutered adult: 1.2 × 183 = 220 kcal.
Grams of the adult food: 220 ÷ 3.8 = 58 g a day.

So the amount falls from 112 g to 58 g, about 48% less, even though the cat has not lost any weight. An owner who changes the bag but keeps scooping 112 g feeds nearly twice the target, and the cat will gain weight quickly. The Kitten Food Calculator and Cat Food Calculator do the sums; the guide to how many calories a cat needs explains each factor.

Switching without an upset stomach

Cats can be fussy about change. Over about a week, replace the old food with the new in steps:

Day	Kitten food	Adult food
1 to 2	75%	25%
3 to 4	50%	50%
5 to 6	25%	75%
7	0%	100%

The percentages refer to calories, not grams, since the two foods differ in energy per gram. A slower change over two weeks suits fussy cats. If your cat refuses the new food, go back a step and slow down; never let a cat go without eating for a long time. If it refuses food for a day, call your vet.

Neutering, spaying and the switch

Many kittens are neutered at around the time of the switch. Both events reduce the energy needed, and they compound. An intact adult at 4 kg needs 277 kcal (1.4 times); the same cat neutered needs 238 (1.2 times), a further 14% fewer. Recalculate after the operation, weigh every one to two weeks for the first couple of months and adjust by about 10% if the trend is wrong. Our guide to weight gain after neutering covers this.

Signs the switch is going well

Stools stay firm within a few days of the change.
Weight is steady, and ribs are easy to feel under a thin layer of padding.
The cat is playful and keen at mealtimes.
Weight on a monthly check moves by less than about 5%.

If the weight climbs steadily, reduce the amount by about 10% and recheck. If the cat becomes thin, ask your vet, since a change in appetite or weight can have medical causes.

Large breeds and slow developers

Some cats are not fully grown at one year. Large breeds can keep growing for longer, and some kittens that had a poor start are late. If your cat is still gaining weight steadily at 12 months, ask your vet whether to continue the kitten food for a while. Even then, you should watch the amount, since a cat that is nearly its full length does not need the full growth ration.

Wet food and mixed feeding at the switch

The same sum works for wet food. A kitten of 3.5 kg eating 448 kcal of a 1,000 kcal/kg wet food gets 448 g a day; the adult at 3.6 kg needs 220 g. If you mix wet and dry, split the calories between them. See wet vs dry cat food for the arithmetic and how many cans of cat food per day for converting to cans.

Treats at the switch

Treats stay within about 10% of daily calories. That allowance halves at the switch. A kitten on 448 kcal has about 45 kcal for treats; the adult on 220 kcal has about 22. If your kitten has been getting a handful of treats, cut them to match. Our guide on how many treats a cat can have shows how many pieces that is at different calorie levels.

Questions owners ask

My kitten is still hungry after the switch. What now? Check the amount against the cat’s weight and the new food’s energy. Appetite and need are not always the same, especially after neutering. Use puzzle feeders, split meals into smaller portions and ask your vet before adding more food.

Can I switch at 10 months because my kitten looks grown? Ask your vet. Looks can mislead, and the vet can judge growth and condition.

Can I use an all-life-stages food? Such foods are labelled as complete for growth and adult maintenance. The amount still has to fall at the switch, because the energy factor does.

What if I have two cats, one a kitten and one an adult? Feed separately where possible, so the adult does not eat the kitten food and the kitten does not get less than it needs. Use separate rooms, timed feeders or microchip-activated bowls.

My vet advised a prescription food. Do the same rules apply? Follow your vet’s feeding instructions, which replace the general method here.

A checklist for switch day

Weigh the cat and note body condition.
Ask your vet to confirm the timing.
Work out the new calorie target and the grams of the new food.
Plan the seven days of mixing, by calories.
Tell everyone in the household the new amounts and the new treat allowance.
Put a reminder in the calendar to weigh after one week and after one month.
Keep the old food until the change is finished, in case you need to go back.

If the cat has been neutered at the same time, mention it to your vet, and use the neutered factor in the calculation. If the cat is on a special diet for any reason, follow your vet’s instructions instead.

How long the kitten amount stays useful

Owners often keep the kitten feeding chart on the fridge long after the cat has grown. Take it down at the switch and replace it with the adult figure. The old numbers are now about double what the cat needs, and an out-of-date chart is a common reason that cats gain weight in their second year.

Quick summary

The AAFP/AAHA kitten stage lasts about the first year; many cats switch to adult food at about 12 months, as your vet advises.
The calorie target drops by about 52% at the same weight (2.5 to 1.2 times resting energy for a neutered adult).
Recalculate grams for the new food: 112 g of a kitten food becomes about 58 g of an adult food in the example.
Switch over about a week, mixing by calories.
Weigh every one to two weeks and adjust by about 10%.
Use the Kitten Food Calculator and Cat Food Calculator.

Frequently asked questions

When should a kitten switch to adult cat food?

The AAFP/AAHA guidelines treat the kitten stage as the first year, so many kittens move to adult food at about 12 months. Your vet may advise a different time for your kitten.

How much less should I feed after the switch?

At the same weight, a neutered adult uses 1.2 times resting energy against 2.5 for a kitten, about 52% less. An intact adult uses 1.4, about 44% less.

How do I switch foods?

Gradually over a week or more, mixing the new food into the old, and recalculate the grams for the new food's energy.

Does neutering change the timing?

Neutering lowers energy needs, so recalculate when it happens. It does not by itself change the life stage.

Can I keep feeding kitten food to an adult?

Kitten food is energy dense, so an adult on the kitten amount is likely to gain weight. Ask your vet before continuing it.

What if my cat is a large breed?

Some cats keep filling out after a year. Ask your vet when to change and how to watch weight.

Sources

Reviewed by the CalcuPaw Veterinary Review Team

Last reviewed 19 Oct 2026 · Meet the review team · This guide is general information, not veterinary advice.