About Pet Calculus
Free calculators for dog and cat owners, built from veterinary sources and honest about what an estimate can and can’t tell you.
Why this site exists
Most pet questions that involve a number get answered with a rule of thumb. Multiply by seven. Double the weight at four months. A little chocolate won’t hurt. Some of those shortcuts are harmless. Some are badly wrong, and a few can put a pet at risk.
Pet Calculus replaces the shortcuts with the real charts and formulas vets use, wrapped in tools that take seconds to use. Each page also explains the math in plain language, so you understand the answer instead of just reading a number.
Where our numbers come from
We only build a calculator when we can base it on a published source we’re willing to link to. In order of preference, we use:
- Veterinary reference texts and professional guidelines, such as the Merck Veterinary Manual and the life stage guidelines from the American Animal Hospital Association (AAHA) and the American Association of Feline Practitioners (AAFP).
- Peer-reviewed research, such as the 2020 DNA-methylation study behind our dog age formula.
- Guidance from established veterinary organizations and hospitals, when the first two don’t cover a question.
We don’t base our formulas on other calculator websites. Every page lists its sources at the bottom, so you can check them yourself.
How we build and check each tool
- The formula is shown on the page. If a result looks odd, you can work through the math yourself.
- Every page includes a worked example. We check those examples by hand against the calculator before publishing.
- Uncertainty is shown, not hidden. Where the science gives a range, as with puppy growth or due dates, the tool shows the range instead of one falsely precise number.
- Safety comes first on health tools. When a result could mean a pet needs care, the page says so plainly and lists who to call.
- Pages are reviewed over time. Each one shows the date it was last reviewed, and we update it when guidance changes.
What these tools can’t do
A calculator can’t examine your pet. Our tools are built to help you understand a situation and have a better conversation with your vet. They don’t diagnose anything, and they never replace a vet who has seen your animal. If your pet seems unwell, call a vet first and use the tools second.
How the site is funded
Pet Calculus is free to use and is supported by advertising. Ads never change a result, and no company can pay to change what a calculator says or which sources we cite. We don’t sell the numbers you type in. In fact, they never leave your browser. See our privacy policy for details.
Spotted a mistake?
We take accuracy seriously, and we’d rather hear about an error than leave it up. If a number looks wrong, a source has been updated, or you have an idea for a new calculator, send us a message. We read every report and update the page’s review date when we make a change.