The short answer for a Domestic Shorthair
A Domestic Shorthair typically stops growing in height and length at around twelve months and finishes maturing — the final broadening of the head and chest and the settling of adult muscle — by roughly eighteen months. The parents, if known, predict the outcome better than any chart, and a kitten whose growth curve flattens smoothly is finishing normally even if the finishing line arrives earlier or later than a neighbour's cat.
Why the mixed-ancestry timeline spreads out
Purebred cats are selected toward a standard, which tightens their growth schedules; nobody has standardised the Domestic Shorthair. Its kittens inherit whatever combination of sizes their mixed parentage hands them, so the population includes petite cats that mature fast and rangy cats that mature slowly, all healthy. Growth in a Domestic Shorthair kitten runs fastest in the first half year, slows through the adolescent months when the cat can look leggy and unfinished, and then trades height for substance.
Reading body condition on a finishing cat
Once a Domestic Shorthair stops growing upward, the useful question changes from how big to how covered. Ribs should be felt easily under a thin layer of fat without showing, and the waist should indent behind them when viewed from above. Check monthly with your hands, because a medium-length shorthair coat hides a great deal from the eye. A cat still gaining visible padding months after its frame stopped growing is not still maturing — it is being overfed for its finished size, and portions should ease down gradually. A cat that thins after maturing, despite eating well, should be booked in with the vet to explore why.
Feeding across the finish line
The switch from kitten food to adult food for a Domestic Shorthair belongs at the point growth levels off, usually around the first birthday, made gradually over a week or so by mixing increasing proportions of the adult food. Kitten food is deliberately energy-dense for building a body; kept going into a finished, neutered, indoor adulthood it quietly builds the wrong thing. Keep feeding times and amounts consistent for a few weeks after the switch, then judge by the rib check and adjust in small steps rather than refilling the bowl on demand through the day.
Slow or lopsided growth: the vet thresholds
See a vet about a Domestic Shorthair kitten's growth if weight stalls or falls for more than a couple of weeks during the fast-growth months, if the kitten is dramatically smaller than littermates and falling further behind, or if growth seems uneven — a body that looks disproportionate, limbs that seem to pain the kitten, or a belly that swells while the ribs show. Appetite loss, persistent loose stools, or low energy alongside poor growth moves the appointment from routine to prompt. Healthy variation in this mixed type is wide, so the trigger is never size alone; it is size plus a change in the kitten's trajectory, appetite, or behaviour. A short written log of weights and appetite makes that trajectory obvious at the appointment.
One record from first weigh-in to adult
A Domestic Shorthair's growth evidence ends up scattered — a breeder or rescue note, clinic weights from vaccination visits, your kitchen-scale figures — and the scatter is exactly what makes later questions hard to answer. Consolidating the weigh-ins as they happen turns maturity questions into a quick look at a curve. A KinsLe Pet Passport keeps those growth entries together with the cat's other records in one portable packet, so any vet can see how this particular Domestic Shorthair grew, not how an average one was supposed to.