A monthly weight, taken the same way every time
An elderly Domestic Shorthair should be weighed about once a month at home, always on the same scales, on a hard flat floor, and at a similar time of day. Weigh her before feeding for consistency, and record the number straight away rather than trusting memory. Month-to-month comparison is the point: a slow drift downward over three readings is a finding, even when each individual change looks too small to mention.
If she will not stand still on scales, weigh yourself holding her and then alone, and use the difference. An elderly Domestic Shorthair who is lifted the same calm way each month gives a usable trend, while a wrestling match gives a number distorted by struggling. Put the scales in a familiar room, not the bathroom she may already dislike, and let her step off the moment you have the reading.
A weekly hands-on check, because eyes deceive
Check an elderly Domestic Shorthair over once a week with your hands, because a medium coat can hide a thinning frame long after your fingers would have found it. Stroke firmly along her ribs, spine, and hips. Ribs should be feelable under a light fat covering without pressing hard, the spine should not feel like a row of knobs, and both sides should feel alike. Note any spot where she tenses, twitches her skin, or turns her head toward your hand.
Add the quick visible checks to the same weekly session. Look in her ears for heavy build-up, at her eyes for discharge or new dullness, and in her mouth if she tolerates a brief lip lift, watching for sore gums, a broken tooth, or bad breath that is new. Part the coat along her back to check skin for scabs or fleas' dirt, and press each claw out gently to confirm none has grown into a circle toward the pad. An elderly Domestic Shorthair who grooms less will often show the first signs in exactly these places.
Track eating, drinking, and the litter tray between checks
Weight alone does not explain itself for an elderly Domestic Shorthair, so keep a simple running note of how much of each meal she eats, whether she drinks more than she used to, and whether the litter tray shows more, less, or looser output than usual. A stable weight with a falling appetite is still a change worth mentioning, and a falling weight with a ravenous appetite tells a different story from a falling weight with no interest in food.
Make the notes where you feed her, on paper or a phone, in a few words at the time. Reconstructing a month of meals at the vet's desk produces guesses, and guesses about an elderly Domestic Shorthair's appetite are rarely accurate in either direction. The habit takes seconds and is the part of home monitoring owners most often skip.
Acting on what the checks show
Book a veterinary appointment sooner rather than later if an elderly Domestic Shorthair loses weight two months running, loses weight quickly, develops a new lump, stops eating, drinks noticeably more, or changes her litter habits and stays changed. A single slightly lower reading with normal appetite and behaviour can be rechecked in a week or two before worrying. The threshold is the pattern, not one number, and a senior cat should never be left losing weight for a season while you wait to see.
Keeping the monthly weights, weekly check notes, and appetite records together in KinsLe Pet Passport gives her veterinarian the full home picture in one packet at her senior visits.