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Pet Weight Change Calculator

Track a weight change over time: percent change, percent per week and whether the pace is inside 1–2% a week.

✔ Reviewed by a licensed veterinarianContent updated 18 Oct 2026Reviewed 18 Oct 2026Sources: AAHA · Pure arithmetic / unit conversion on user inputs
Pet Weight Change CalculatorFree · instant
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Quick answer. A dog that went from 30 kg to 28.5 kg in 5 weeks lost 5% of its weight, 1% a week, which is inside the 1–2% a week pace commonly recommended for weight loss. Faster than about 2% a week is a reason to talk to your vet.

How to use the pet weight change calculator

  1. Enter the starting weight and the current weight.
  2. Enter how many weeks passed between them.
  3. Press Calculate.

Worked example

A dog that went from 30 kg to 28.5 kg over 5 weeks.

Starting weight
30 kg
Current weight
28.5 kg
Weeks between the two weights
5
-5% (loss)
Per week
-1%
Kilograms per week
-0.3 kg
Pace
Inside the 1–2% a week pace commonly recommended for weight loss

The 1–2% a week range is from AAHA (2014) guidance on weight loss. Your vet sets the plan.

Example values are illustrative; this result is produced by the same calculator above.

How we calculate it

total % = (current − start) ÷ start × 100; per week % = total % ÷ weeks; pace compared with AAHA's 1–2% of body weight per week

Sources: AAHA · Pure arithmetic / unit conversion on user inputs (no external constant)

Understanding your result

Tracking weight over time shows whether a diet is working. Enter the starting weight, the current weight and the weeks between them. The calculator shows the percent change, the percent per week and the kilograms per week.

For weight loss, the pace commonly recommended for dogs is about 1 to 2% of body weight per week (AAHA 2014). A dog that went from 30 kg to 28.5 kg in 5 weeks lost 5%, or 1% a week, which is inside that range.

Faster than about 2% a week is a reason to talk to your vet, because rapid loss can signal illness or an overly strict diet. A positive percentage means weight gain.

Common mistakes

  • Weighing on different scales or at different times of day.
  • Entering the wrong number of weeks.
  • Expecting a steady loss every week; weights fluctuate.
  • Cutting food sharply to speed up weight loss.
  • Not discussing the plan with the vet.

Good to know

  • Weigh your pet every two to four weeks at the same time of day.
  • Use the Dog Weight Loss Calculator for a calorie target.
  • Cats must lose weight especially slowly; follow your vet's plan.

When to talk to your vet

  • Weight loss faster than about 2% a week
  • Unexplained weight change
  • Before starting any diet

Frequently asked questions

How fast should a pet lose weight?

About 1–2% of body weight per week is a commonly recommended pace for dogs (AAHA 2014). Your vet sets the plan for your pet.

What if my pet is losing weight faster?

Faster than about 2% a week is a reason to speak to your vet, because rapid loss can be a sign of illness or an overly strict diet.

Can I use it to track weight gain?

Yes. A positive percentage means weight gain. The pace message refers to the 1–2% a week range for weight loss.

Why compare with 1–2% a week?

AAHA (2014) weight-management guidance suggests that pace for dogs. Your vet sets the right pace for your pet.

Can I use pounds?

Yes. Switch the unit toggle to imperial and enter both weights in pounds.

What if the weight goes up?

The calculator shows a positive percentage and does not call it a weight-loss pace.

Reviewed by a licensed veterinarian
Last reviewed 18 Oct 2026 · How we review

Sources

  1. AAHA (2014) Weight Management Guidelines for Dogs and Cats
  2. Pure arithmetic / unit conversion on user inputs (no external constant)
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Estimates only. Every pet is different — confirm with your veterinarian. If your pet may have eaten something harmful, contact your vet or an animal poison helpline now.