Puppy food is more calorie-dense and higher in protein, fat, calcium, phosphorus and DHA than adult food, because a growing animal needs more of everything.
Once growth finishes, those same qualities become a route to obesity.
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When to switch
Timing follows expected adult size, because bigger dogs grow for longer.
- Small breeds (under 10kg): 9 to 12 months
- Medium breeds (10 to 25kg): around 12 months
- Large breeds (25 to 45kg): 15 to 18 months
- Giant breeds (over 45kg): 18 to 24 months
A useful practical marker: switch when your dog has reached roughly 90 percent of their expected adult weight and growth has visibly slowed.
Why timing matters in both directions
Too early means a growing puppy on a diet that does not meet growth requirements. In a large breed still laying down bone at fourteen months, that matters.
Too late means an adult dog eating a calorie-dense growth diet. Puppy food can carry considerably more calories per gram than adult maintenance food, and a dog who has stopped growing but keeps eating it gains weight quickly.
Neutering changes the numbers
Metabolic rate drops noticeably after neutering — estimates commonly cited are a reduction of somewhere around 20 to 30 percent in energy requirement.
If your dog is neutered before the food switch, the food does not change but the portion should. Reduce by roughly ten to twenty percent at the time of neutering and monitor body condition closely over the following months.
This is the single most common point at which dogs begin to gain weight, and it is entirely preventable by adjusting the amount rather than waiting to see what happens.
How to switch
Over seven days, or ten for a sensitive dog:
- Days 1–2: 75% puppy food, 25% adult
- Days 3–4: 50/50
- Days 5–6: 25% puppy, 75% adult
- Day 7 onwards: 100% adult
Mix them thoroughly in the same bowl. A dog who can separate them will eat only the one they prefer.
Some softer stool for a few days is normal. Watery diarrhoea, blood, vomiting or lethargy is not — stop, go back to the previous food, and ring your vet.
Recalculating the portion
Do not carry over the puppy portion. Work it out again.
- Find the kcal per kilogram figure on the new food’s packaging
- Use a calorie target for your dog’s ideal adult weight — your vet can give you one, or use resting energy requirement multiplied by roughly 1.6 for a neutered pet dog
- Divide the target by the food’s calorie density to get grams per day
- Weigh it. Measuring cups produce large errors, and studies of owners using scoops have found discrepancies of up to 80 percent
Then adjust by body condition every two weeks: ribs easily felt under a thin covering, a visible waist from above, and a tuck from the side.
What changes in the bowl
Expect the volume of food to drop noticeably. Adult food is less calorie-dense, but the calorie target falls more than the density does, so most dogs eat less overall.
Many owners find the adult portion looks alarmingly small and quietly overfeed. Trust the scales and the body condition, not the appearance of the bowl.
Meal frequency
Most dogs move to two meals a day by around six months, so no change is usually needed at the food switch.
Small breeds and deep-chested dogs may do better on three.
Choosing the adult food
The criteria that matter:
- Complete and balanced for adult maintenance, meeting AAFCO or FEDIAF profiles
- Made by a company that employs a qualified nutritionist and runs feeding trials
- Appropriate calorie density for your dog’s activity level
- Something you can reliably buy
Criteria that matter less than marketing suggests: an ingredient list that appeals to a human, the absence of a currently unfashionable ingredient, and terms like “ancestral” or “human grade”, which have no regulatory meaning in pet food.
If your puppy has done well on a food, staying within the same brand’s adult range is a reasonable default — the formulation philosophy is consistent and the transition tends to be smoother.
Storage, which affects palatability
Buy a bag size you will use within about six weeks of opening. Fats oxidise, and stale food is less palatable and less nutritious — one of the more common hidden reasons a dog goes off a food they previously liked.
IRIS USA Airtight Pet Food Storage Container
Airtight storage with a sealing lid. Put the whole bag inside rather than tipping the kibble in — the bag has its own fat barrier, and you keep the batch code in case of a recall.
Large-breed specifics
If your dog will mature over about 25kg, stay on a large-breed puppy formula until the switch, and never add calcium or a general growth supplement to a complete food. Excess calcium during growth is directly linked to developmental orthopaedic disease.
When you do switch, a large-breed adult formula with controlled calories and joint support ingredients is a reasonable choice — though keeping the dog lean matters considerably more than which bag it comes from.
The three months after the switch
Weigh your dog monthly. This is the period when weight gain creeps in unnoticed: growth has stopped, activity often falls as adolescence settles, and portions have not been reassessed.
Catching a kilo early is trivially easy. Catching five kilos two years later takes four months of dieting.
