A senior cat can lose condition almost invisibly. Her coat still shines, her appetite seems unchanged, and because you see her every day, the slow thinning along her spine registers as nothing at all until a visitor remarks on it. Regular weighing replaces that guesswork with a line of numbers, and the line matters more than any point on it. In stable health, a monthly weighing is frequent enough to catch a drift while it is still small. If she is underweight, following a feeding plan, or under active monitoring for a known concern, the rhythm tightens to fortnightly, because a cat already short of reserves has less margin before a loss becomes significant.
A Method That Stays Comparable
A weighing is only useful if the next one is taken the same way, so fix the variables once and keep them fixed. Use the same scales each time, on the same hard surface, since a scale sitting on carpet reads differently from one on a kitchen floor. Weigh at the same point in her day, ideally before a meal rather than after one, and before she has just emptied her litter tray or just filled her stomach, both of which move the number by more than the change you are watching for. If she will not stand on scales alone, weigh yourself holding her, then weigh yourself without her, and subtract; a carrier works the same way if you weigh the empty carrier once and deduct it every time. Write the result down with the date immediately, because a remembered weight quietly improves or worsens in the retelling, and the log is the whole point of the exercise.
Reading a Trend Instead of a Number
Single readings wobble. A big drink, a recent meal, a full bladder and a nervous crouch on the scales can each shift the figure, which is why one low reading should trigger a recheck at the next session rather than alarm. The signal worth trusting is direction repeated over time: three readings easing downwards, or a line that climbs steadily while her food stays the same, tells a true story even when each step is tiny. Put the figures in a simple list or chart where the shape is visible at a glance, and feel along her ribs and spine when you lift her, because condition you can feel backs up condition you can measure. A cat whose weight holds steady while her back grows bonier may be trading muscle for fat, and that is a conversation for the vet even though the headline number never moved.
The Size of Change Worth a Phone Call
As guidance, a shift of around five percent of her weight either way is worth mentioning to the vet, promptly if it arrives quickly or alongside other changes. Percentages keep the judgement honest across sizes: on a small senior cat, five percent is a couple of hundred grams, an amount no eye would catch, while on a larger cat it is a more substantial loss that still deserves the same call. Loss paired with eating well is never a wait-and-see combination, and neither is loss with increased thirst, vomiting, or a cat who has stopped jumping to places she used to reach easily. The vet would always rather hear about a five percent drift from an owner holding a dated log than meet a much thinner cat whose decline nobody can date. Mention it at her next senior check if the drift is slow and she is otherwise herself, and phone sooner when the change is fast or company arrives with it.
Those dated figures become far more useful when they travel with her instead of living in a kitchen notebook. Pet Passport is where her weigh-ins live inside KinsLe, a single record the practice can read at a glance alongside the rest of her history.