Free Pet Weight Change calculator with clear step-by-step results.
Absolute weight change tells you little about a pet without the percentage: 2.5 kg is a modest shift for a 30 kg dog but a serious one for a 5 kg cat. The weekly rate is what clinicians watch, because safe loss is typically 1-2% of body weight per week for dogs and around 1% for cats, and unintentional loss at any rate warrants investigation. The projection assumes the current rate continues, which in practice slows as the animal approaches its target.
Change and rate
Change = current − start; weekly rate % = change ÷ weeks ÷ start × 100
Projection
Weeks to target = |current − target| ÷ |change per week|, when the trend heads toward the target
Unexplained weight change in an animal can indicate serious illness. Have any unintentional loss or gain assessed by a veterinarian rather than managed from a calculator.
Any unexplained loss, and loss faster than about 2% of body weight per week even when intended. Unintentional weight loss can indicate hyperthyroidism, diabetes, kidney disease, dental pain or parasites and should be investigated rather than welcomed.
Because the trend is flat or moving away from the target, so no honest completion date exists. Rather than return a misleading number, it reports zero — the plan needs changing, not extrapolating.
Every two to four weeks on the same scale at the same time of day. Weekly readings on a home scale are dominated by measurement noise, especially for small animals.