How many days should the food change take?

In a healthy animal the classic scheme spreads the change over about a week, raising the share of new food every two or three days. It is not a rigid rule: a sensitive stomach or a move to a very different food needs ten or twelve days. The right length is whatever lets you reach the new food without loose stools.

Should I increase the amount when I move to a different food?

The transition is about the type of food, not the amount. Start from the daily ration already correct for your animal and apply the proportions to that. If the new food has a very different energy density, the ration may need recalculating, but that is a separate calculation to do with the vet, not an increase decided by eye.

My dog has loose stools on day three: do I continue?

No, do not move the percentage up while an upset is present. Go back to the previous day's proportion and stay there a couple of extra days before trying again. If the stools stay liquid beyond a day or two, if blood appears or if the dog is dull, stop the transition and consult the vet.

The cat refuses the new food: what do I do?

Many cats are wary of change. Lower the new food share to a percentage it accepts and move up far more slowly, mixing the two foods well. Do not let it fast waiting for it to give in: a cat that eats much less for more than a day should be assessed by the vet, because prolonged fasting in cats is dangerous.

Can I do the transition while the animal is on treatment?

In that case talk to the vet first. An animal on treatment, sick, young or elderly may have particular needs, and sometimes the diet change is part of the care plan itself. The gradual transition remains the method, but the choice of food and the right timing should be agreed, not decided alone.

Practical feeding10 minLevel: BeginnerUpdated on August 5, 2026

Switching your dog's or cat's food without stomach upset

How to move from one food to another with a gradual transition, the day by day mixing schedule, and the signs that tell you to slow down or stop.

Audience: Pet owners
Species: Dog, Cat
Scope: Valid everywhere

What you need before you start

Il vecchio alimento ancora disponibile in quantità sufficiente per una transizione di più giorni
Il nuovo alimento già scelto, meglio se dopo un confronto con il veterinario sulle esigenze dell'animale
Una bilancia da cucina per pesare le porzioni invece di stimarle a occhio
Un quaderno o una nota sul telefono per segnare le proporzioni del giorno e l'aspetto delle feci

Suddenly changing a dog's or cat's food is one of the most common ways to end up with loose stools, bloating or a refused bowl. The reason is that the digestive tract and the gut flora are used to a certain food, and an abrupt switch asks them to adapt overnight. The answer is not a miracle product but a slow method, the gradual transition: you mix a rising share of the new food with a falling share of the old one over several days, giving the system time to adjust. This guide gives you a mixing schedule, explains how to weigh the proportions rather than eyeball them and, above all, how to read stools and appetite to know when to go on, when to slow down and when to stop. One caveat always applies, a diet change for a sick, very young, elderly or ill animal should be decided with the vet, not on your own.

Why the transition should be slow

In the gut lives a population of microorganisms that helps digestion and specialises around the usual food. When the food changes all at once, this population has no time to adapt, and the typical result is a faster transit with loose stools, sometimes bloating or vomiting. A transition spread over several days lets the flora rebalance gradually, cuts the risk of upset and also makes it easier to tell whether the new food is tolerated. That is why haste, in this case, works against you.

The transition schedule

The classic scheme spreads the change over roughly a week in a healthy animal, raising the share of new food every two or three days. It is not a rigid rule but a starting point: an animal with a sensitive stomach, or a switch to a very different food, needs a slower pace. The percentages apply to the daily ration already correct for your animal, not to an increased amount.

Indicative scheme for a healthy animal, slow down if needed
Phase	Old food	New food
Days 1 and 2	About three quarters	About one quarter
Days 3 and 4	About half	About half
Days 5 and 6	About one quarter	About three quarters
Day 7 onward	None	All the new food

The day by day procedure

Weigh the whole daily ration
Start from the total amount correct for your animal and weigh it on the scale. The transition proportions are calculated on this ration, not on an increased amount: you change the type of food, not how much you give.
Split the two shares and mix them
Weigh the old and new food shares set by the phase and mix them well in the bowl, so the animal cannot separate the pieces and pick only the familiar ones.
Spread across the usual meals
Keep the same number of meals and the same times as always. Changing food, amount and timing at once would take away your ability to see what causes any upset.
Watch stools, appetite and behaviour
Each day look at the consistency of the stools, whether the bowl is finished and whether the animal is as lively as usual. These are the three signs that tell you if you can move to the next phase.
Move up only if everything is normal
Move to the next proportion only when stools and appetite have been normal for a couple of days. If something is off, stay put or drop back one phase.
Note the proportions and any changes
Record each day the percentage used and how it went. If you need to discuss it with the vet, a precise diary is worth far more than a vague memory.

Reading stools and appetite

During the transition, stools and appetite are your compass. A slight passing softening may settle on its own, but some signs clearly say to slow down, and others to stop and consult the vet. The practical rule is never to move up a phase while an upset is under way.

Sign, what to do and when to call the vet
Sign	What to do	Watch out
Slightly softer but formed stools	Stay at the current phase one more day	Usually settles on its own
Liquid stools or diarrhoea	Go back to the previous proportion	If it lasts over a day or two, consult the vet
Repeated vomiting	Stop moving up and contact the vet	Not a normal adjustment
Refusing the bowl for more than a day	Go back to an accepted proportion	In cats this needs urgent assessment
Blood in the stools or dullness	Stop the transition and see the vet	A sign beyond a diet change

Common mistakes when changing food

Switching overnight with no transition, which is the most common cause of loose stools.
Increasing the ration because the new food is more appealing: you change the type, not the total amount.
Changing food, timing and number of meals together, so you can no longer tell what causes an upset.
Adding treats or leftovers during the transition, which confuse the reading of the stools.
Pushing the percentage up while an upset is under way, instead of slowing down.
Deciding a diet change on your own for a sick, young, elderly or ill animal: in those cases the choice and the timing are set by the vet.

Frequently asked questions

How many days should the food change take?: In a healthy animal the classic scheme spreads the change over about a week, raising the share of new food every two or three days. It is not a rigid rule: a sensitive stomach or a move to a very different food needs ten or twelve days. The right length is whatever lets you reach the new food without loose stools.
Should I increase the amount when I move to a different food?: The transition is about the type of food, not the amount. Start from the daily ration already correct for your animal and apply the proportions to that. If the new food has a very different energy density, the ration may need recalculating, but that is a separate calculation to do with the vet, not an increase decided by eye.
My dog has loose stools on day three: do I continue?: No, do not move the percentage up while an upset is present. Go back to the previous day's proportion and stay there a couple of extra days before trying again. If the stools stay liquid beyond a day or two, if blood appears or if the dog is dull, stop the transition and consult the vet.
The cat refuses the new food: what do I do?: Many cats are wary of change. Lower the new food share to a percentage it accepts and move up far more slowly, mixing the two foods well. Do not let it fast waiting for it to give in: a cat that eats much less for more than a day should be assessed by the vet, because prolonged fasting in cats is dangerous.
Can I do the transition while the animal is on treatment?: In that case talk to the vet first. An animal on treatment, sick, young or elderly may have particular needs, and sometimes the diet change is part of the care plan itself. The gradual transition remains the method, but the choice of food and the right timing should be agreed, not decided alone.

What to do next

Change the food calmly: spread the switch over a week or more, mixing a rising share of new food with a falling share of the old, always on the same daily ration. Watch stools, appetite and liveliness every day, move up a phase only when all is normal, and slow down or stop at the first signs, consulting the vet for sick, young, elderly or treated animals.