How to Switch Cat Food: The 7-Day Schedule, With Grams

Switch over seven days, in four steps: 25% new food for days 1–2, 50% for days 3–4, 75% for days 5–6, and 100% on day 7. A cat with a sensitive gut or a history of diet-related diarrhoea gets ten to fourteen days. The schedule matters because the hindgut bacteria and the pancreatic proteases need roughly a week to adjust, and a sudden change produces loose stool within 24–48 hours — usually on your carpet, at night.

The seven-day schedule in grams

Assume a 4 kg cat eating 60 g of kibble a day. Work in grams, not scoops, and mix thoroughly rather than layering new food on top.

Day	Old food	New food	What to watch
1–2	45 g	15 g	Appetite, stool form
3–4	30 g	30 g	Any vomiting after eating
5–6	15 g	45 g	Stool firmness, gas
7	0 g	60 g	Intake over 24 hours

For a cat on wet food, the same proportions apply by weight: 190 g a day becomes 140 g old plus 50 g new on days 1–2. Do not switch the treat brand in the same week; if something goes wrong you will not know which change caused it.

Why not just swap the bowl

The large intestine holds a dense bacterial population that ferments fibre and produces short-chain fatty acids, and that population shifts with the substrate it is given. Full turnover takes seven to fourteen days. Pancreatic and brush-border enzymes follow a similar curve, and a cat moved from 30% fat to 22% fat overnight may simply not secrete enough lipase for the new load.

The result is osmotic and fermentative diarrhoea: stool that goes soft within a day, turns yellow and sour-smelling by day two, and resolves on its own in three to five days if you stop pushing. Vomiting within 30 minutes of eating is different — that is usually volume or texture, not flora, and it means slow down rather than stop.

Converting between wet and dry by calories

Never match wet and dry by weight; the water content makes the numbers meaningless. Match calories. A kibble at 4,000 kcal/kg delivers 80 kcal in 20 g. A pâté at 90 kcal/100 g delivers 80 kcal in 89 g. So 20 g of dry food is replaced by roughly 89 g of canned — a four-and-a-half-fold weight increase for the same energy.

This is where most dry-to-wet transitions go wrong: the owner serves 89 g of pâté next to the usual 60 g of kibble, the cat eats 350 kcal instead of 240, and gains 500 g in a month. Set the total first, then split it.

Getting a picky cat to accept the new food

• Warm it. Most wet food is most palatable at 37°C. Ten seconds in the microwave, stirred, tested with a finger.
• Start at one teaspoon. A tablespoon of new food mixed into a full meal is enough for day one if the cat is suspicious.
• Use a fifteen-minute window. Put the food down, take it away after 15 minutes. Free-feeding a refused meal teaches the cat that refusal works.
• Never fast a cat for more than 24 hours. Overweight cats can develop hepatic lipidosis after 48–72 hours without food, and it is fatal without aggressive treatment.

If diarrhoea starts

Go back one step for three to five days, then resume at half the previous increment. Add a teaspoon of plain cooked pumpkin per 5 kg of body weight for fibre, and a probiotic at 5–10 billion CFU a day for a week. Keep water available in three places; diarrhoea dehydrates faster than owners expect.

See a vet if there is blood, if the cat stops eating, if diarrhoea lasts past 48 hours, or if a kitten under six months is affected — kittens decompensate in a day.

Special cases that need a different schedule

A suspected food allergy needs a hydrolysed or novel-protein diet with no other protein source for eight to twelve weeks. That means no treats, no scraps, no flavoured toothpaste, and other cats in the house eating the same food if possible. Twelve weeks is the number because skin and gut need a full turnover cycle to show improvement.

For kidney disease or diabetes, change one variable at a time with the vet, and recheck bloodwork two to four weeks after the switch rather than the same week.

What to track during the switch

Weigh the cat weekly; a drop of more than 2% of body weight in a week means the new food is not being eaten enough. Score stool on a seven-point scale where 2–3 is ideal, and note it daily. Vomiting more than twice a week, or any vomiting with lethargy, is a stop signal.

Once the switch is done, keep the old brand's name written down. If you need to go back, you want the exact formula, not a memory of a bag colour. More on portion sizes and weight targets sits in our care section and the calculator.

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