Pet Weight Change
Free Pet Weight Change calculator with clear step-by-step results.
About Pet Weight Change
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.
Formulas
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
Worked example
With the default values below, Pet Weight Change returns Weight Change of -2.50. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Starting weightminimum 0.1 kg
- 30 kg
- Current weightminimum 0.1 kg
- 27.5 kg
- Weeks since the starting weightminimum 0.5 weeks
- 10 weeks
- Target weightminimum 0.1 kg
- 25 kg
Results
- Weight Change
- -2.50 kg
- Change Against Starting Weight
- -8.33%
- Rate of Change per Week
- -0.83%
- Weeks to Target at This Rate
- 10.0 weeks
Step by step
- 1Values used
- 2Change and rate
- 3Projection
- 4Weight Change= -2.50 kg
- 5Change Against Starting Weight= -8.33
- 6Rate of Change per Week= -0.83
- 7Weeks to Target at This Rate= 10.0 weeks
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- 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.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
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.
Frequently Asked Questions
When is weight change a concern?
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.
Why does the projection show zero sometimes?
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.
How often should I weigh a pet on a plan?
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.