Cats hate sudden change, and nowhere is that clearer than in the food bowl. Switch a cat food overnight and the likely results are a refused meal, vomiting, loose stool, or a cat that simply walks away and waits for the old food to return. A slow transition over 7 to 10 days avoids almost all of that. This planner builds the mixing table for you in grams, day by day, and lets you download it as a printable PDF to stick on the fridge.
The schedule follows the standard veterinary pattern. For a 7 day plan, days 1 and 2 are 75 percent old food and 25 percent new. Days 3 and 4 move to half and half. Days 5 and 6 are 25 percent old and 75 percent new. Day 7 is fully new food. The 10 day plan stretches the same phases: days 1 to 3 at 25 percent new, days 4 to 6 at half, days 7 to 9 at 75 percent new, and day 10 fully new. Cats with sensitive stomachs should use the 10 day plan, or even slower.
Why does the gut need this time? The bacteria in the intestine are tuned to the current food, including its protein source, fat level, and fibre type. A new food changes all of those at once, and the gut bacteria need days to adjust. A sudden switch overwhelms that adjustment and produces gas, soft stool, and nausea. Mixing gives the gut a gradual introduction, so the bacteria shift step by step instead of all at once. This is normal biology, not fussiness.
Here is a worked example. A cat eats 60 grams a day and moves to a new food over 7 days. Day 1 is 45 grams old and 15 grams new. Day 3 is 30 grams of each. Day 5 is 15 grams old and 45 grams new. Day 7 is 60 grams new. The total stays 60 grams every day, which matters: the transition changes the mix, not the amount. If the new food has very different calories per 100 grams, adjust the total separately using a calorie calculator, but keep the mixing ratios from the table.
Weighing beats scooping here too. The ratios only work if both foods are measured in grams. A scoop of one kibble can weigh a different amount from a scoop of another, because kibble size and density vary. Use a kitchen scale, mix the two foods in the bowl, and serve at the usual meal times. If the cat picks out the old kibble and leaves the new, try mixing wet food of the new type, or crushing a little new kibble over the old, to make separation harder.
What if the cat refuses the new food entirely? First, slow down: stay on the current step for two or three extra days instead of moving on. Warming wet food slightly releases more smell and often helps. Never starve a cat into eating a new food. A cat that eats nothing for 24 hours, especially an overweight cat, is at risk of liver disease and needs a vet, not more pressure. If refusal lasts more than a few days, the new food may simply not suit the cat, and another product is the honest answer.
Watch the stool during the transition. Slightly softer stool for a day or two at a step change is common and usually settles. Watery diarrhoea, vomiting more than once, blood in the stool, or a cat that stops drinking needs a vet promptly. Keep a simple note each day: appetite, stool, and any vomiting. The PDF from this planner has room in spirit for those notes, and the pattern over days tells a vet far more than a single bad day.
Special cases need care. Kittens moving to adult food, cats moving to a vet prescription diet, and cats changing from dry to wet food all benefit from the same slow pattern, but the reasons differ. A prescription diet change is often urgent, so ask the vet how fast to go: sometimes a faster switch is medically right even if the stomach complains. A dry to wet change also changes water intake, which is usually a good thing, but watch the portion, because wet food grams are much larger for the same calories.
Storage matters during a switch. Keep both bags sealed and fresh, and do not mix large batches in advance, because the mixed ratio changes daily. Buy a small bag of the new food first, so a refusal does not waste a large bag. If the new food is a different shape or size of kibble, check that senior cats and cats with dental problems can manage it before committing to the full bag.
To sum up, switching cat food is a week-long project, not a single meal. Build the table with this planner, weigh both foods, move one step at a time, and print the PDF so everyone feeding the cat follows the same day. Slow is not fussy. Slow is how a cat gut works.