It's a Tuesday evening. The cat's on the bathroom scale because you read somewhere that senior cats lose weight quietly, and the number that came up is 10.8 lb. Last week at the clinic they wrote 13.8 on the discharge paper. Your first thought is that the scale is wrong. Your second, slower thought is that 3 lb is a fifth of a cat, and if the cat's scale reading is telling the truth, that's the whole conversation you need to have with your vet this week.
Three pounds on a 15 lb cat is roughly 20% of body weight. Clinical thresholds put a 5% unintentional change in the flag-it column; this is four times that. If it's real, it's real. If the home scale is off by 3 lb, that's also worth knowing before the next wellness visit. Either way, the number in front of you is information. What's missing is the pattern around it: what the scale has read across the last few weeks, what the cat has been eating and drinking, what else has changed. A single reading is a snapshot. A log is how the picture gets built.
That's what the tracker below is for. It runs in your browser, stores the log on your device, and shows the trend across your last five entries. No signup, no account, nothing leaves your browser until you export. When Veta ships on iOS, the same log becomes a field on your pet's passport and the trend line travels across every recheck and every clinic. Today it's a notepad with math. That's enough to start.
Why the trend matters more than any single reading
The single most useful thing a weight log does is turn numbers into a line. A pet who's been holding steady at 62 lb for six months and drops to 59 lb over four weeks tells you something that any one of those readings never will on its own. 59 alone is just a number. 62 to 59 across four weeks is a 5% drop, and the 5% threshold is where most clinicians move from acknowledging the reading to asking what's behind it. AAHA's 2021 nutrition and weight management guidelines treat unintentional weight change as a clinical workup signal, which is why the conversation usually starts well before a pet has lost a meaningful fraction of their body weight.
Direction matters more than absolute number. A 60 lb Labrador who gains a pound over a snowy winter probably needs more walks in March, not a workup. The same Lab who loses six pounds across a month while eating his full bowl is carrying a different kind of signal; rapid loss with a preserved appetite is one of the older flags for diabetes, early kidney disease, or hyperthyroidism in older dogs across standard veterinary references. Neither of those rules out a simpler explanation, and neither is a diagnosis. What they are is a good enough reason to move the next clinic call from “at the next wellness visit” to “this week.”
Obesity in dogs and cats is one of the most common preventable conditions in small-animal practice, and the veterinary literature has published repeatedly on the cost of excess body fat: shorter median lifespan, higher rates of joint disease, harder anesthesia, earlier onset of diabetes in cats. The 14-year Labrador lifespan study (Kealy and colleagues, the Purina-funded longitudinal work published in JAVMA in 2002) found that dogs fed to maintain lean body condition lived a median of 1.8 years longer than littermates kept in the normal US range, which is to say overfed. That study keeps getting cited because the signal is large and the intervention is simple; the tool is a scale, and the habit is a log.
How to weigh at home honestly
The point of a home weigh-in log isn't clinical precision. It's repeatable consistency. A bathroom scale that reads half a pound heavy is fine, as long as it reads half a pound heavy every time. The trend line carries the signal even when any one reading drifts. The four habits that make a home log actually useful are all about controlling the conditions around the reading: same scale, same time, same surface, same routine.
Same scale first. Pick one. For medium and large dogs a standard bathroom scale works best; for small pets under about 20 lb, a kitchen scale with a broad platform or a digital infant scale reads cleaner than most cheap pet scales. Wherever the scale lives, it lives there. Moving the scale to a carpeted floor, a slightly soft mat, or a warped tile all change the reading in a consistent direction. If the scale moves, note it in the log.
Same time of day, second. Before breakfast, after the first bathroom stop, is the cleanest slot. A dog who has eaten a meal and drunk a bowl of water can weigh half a pound heavier twenty minutes later. Cats are worse because their feeding and drinking pattern is more variable across the day. The routine to beat is “I weigh when I remember.” A Tuesday-morning habit beats sporadic every time.
Hold-and-subtract, third. Small pets who won't sit still for a scale get weighed by you. Step on the scale alone, write the number, pick up the pet, step on again, subtract. Repeat twice and average the two. For cats in carriers, a weigh-the-carrier-empty-once habit lets you drop the cat in, step on the bathroom scale with the carrier, subtract the carrier weight, and get a clean number without the cat ever having to like the scale.
Last, one line of context per reading. Whether the pet ate, whether a medication changed this week, whether anything obvious is up. The note field in the log takes about ten seconds to fill. A log with notes reads ten times faster at the recheck than a log with only numbers, because the notes tell your vet which small variations matter and which are background noise.
Body condition score: the companion number
The scale reads fat and muscle together. Body condition score, abbreviated BCS, reads them separately. The distinction matters because a pet can lose three pounds and hold BCS steady (the loss is fat, the body is rebalancing) or lose nothing on the scale while BCS drops a full point (muscle is going, fat is replacing it, a common early pattern in senior cats with kidney disease). One number without the other misses half the picture.
The standard US scale is 9-point: 1 is severely underweight, 5 is ideal, 9 is severely obese. WSAVA, which is the World Small Animal Veterinary Association and publishes the global nutritional assessment guidelines, built the chart most US clinics use. The check is physical and quick: feel the ribs (you should feel them easily, with a thin fat cover), look from above for a visible waist behind the ribcage, and look from the side for a tuck-up in the belly. A pet at BCS 5 has all three signs; at BCS 7, the ribs take pressure to feel and the waist is gone; at BCS 3, the ribs are prominent and the spine is visible under thin muscle. The clinic-ready nutritional-assessment workflow most US vets use at the exam cross-references BCS with weight management planning, which is why scoring alongside the scale is the standard the exam room actually runs on.
Running BCS at home is not a substitute for the clinic's read. Your vet is better at it than you are, and the physical exam includes a muscle-condition score most owners don't attempt. What home BCS gives you is the ability to see the same three signs you saw last month. If the waist looks gone this week and was there last time, that's information. Monthly BCS, logged alongside the scale number, is the cadence most hospice-oriented and senior-care vets recommend. The tool above accepts a BCS on any entry, and prompts you when the last one was thirty days back.
The tracker
Everything above is the framing. The tool below is where the log actually happens. Enter a pet name, pick the species, add the breed if you want the dropdown to suggest, pick the date, enter the weight in the unit your scale uses, and add a note if there's context worth holding. The trend line and the percent-change readout update as you add entries. The BCS prompt surfaces when it's been a month since the last one.