How we calculate

Last updated: October 25, 2026

Our rules

1. Published methods only. Every formula and reference value comes from a veterinary association (AVMA, AAHA, AAFP, WSAVA), the Merck Veterinary Manual, a university veterinary school, a peer-reviewed study or, for costs, the ASPCA. We don't invent formulas or "adjust" published numbers.
2. Every source is dated. Each calculator lists its sources and the date we last opened them and checked the numbers.
3. The math is shown. Each page explains the formula step by step, with worked examples and tables, so you can check the result by hand.
4. The examples are tested. An automated test runs the calculator code on every worked example and fails if a page and the code disagree.
5. Limits are stated. Each page ends with what the method can't tell you. Where we couldn't find a reliable published method, we don't offer a calculator.
6. Health questions go to your vet. Health-related pages carry a visible note: the result is an educational estimate, not veterinary advice.

What we left out, and why

• Chocolate toxicity calculator. Toxic doses depend on the type of chocolate, the exact amount and the dog. A calculator that shows "low risk" could delay treatment. If your dog has eaten chocolate, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 (a fee may apply) right away.
• "Feed 2–3% of body weight" for raw diets. We found this rule only on raw-food sellers' and hobby sites, not in a veterinary reference, so the raw dog food calculator works from calories and the food's label instead.
• Crate size by weight. Weight-based crate charts come from crate sellers and differ by brand; the crate calculator uses the AKC's measuring method and the IATA formula.
• Dog harness size chart. Harness sizes are set by each brand; the AKC's advice is to measure chest girth and use the maker's own chart, so we don't publish a generic one.
• Dog exercise needs by breed. AAHA's weight-management guidelines say evidence is lacking to describe an ideal exercise program for dogs. Minute-by-breed tables online aren't from veterinary sources.
• Puppy growth percentile charts. The WALTHAM charts (Salt et al. 2017) publish their centiles only as images, so we can't cite their numbers; the puppy weight calculator uses breed curves published with their parameters (Hawthorne et al. 2004).
• "1 pound per month" for kittens. Often repeated, but not from a veterinary reference. The kitten chart uses the ASPCA's published ranges.
• Pregnancy and nursing in the food calculators. Needs change week by week; a fixed factor would mislead. Your vet should plan this.

Who checks this

The site is built by an IT technician, not a veterinarian (see about). That's why we stick to published methods and show our work. If you're a veterinary professional and spot an error, please tell us.

All sources

• American Kennel Club (AKC). How to Calculate Dog Years to Human Years (size-based dog age chart). Checked October 25, 2026.
• American Veterinary Medical Association (AVMA). Pets age faster than people (poster). Checked October 25, 2026.
• Wang T, Ma J, Hogan AN, et al. Cell Systems 11(2). Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome (2020). Checked October 25, 2026.
• UC San Diego Today. How old is your dog in human years? Scientists develop better method than "multiply by 7" (2020). Checked October 25, 2026.
• International Cat Care. How to tell your cat's age in human years. Checked October 25, 2026.
• American Association of Feline Practitioners (AAFP) and American Animal Hospital Association (AAHA). 2021 AAFP/AAHA Feline Life Stage Guidelines (2021). Checked October 25, 2026.
• Merck Veterinary Manual. Nutritional Requirements of Small Animals. Checked October 25, 2026.
• The Ohio State University Veterinary Medical Center, Nutrition Support Service. Companion Animal Nutrition Support Service: estimating Calorie needs. Checked October 25, 2026.
• American Animal Hospital Association (AAHA). AAHA Nutritional Assessment Guidelines for Dogs and Cats (2010). Checked October 25, 2026.
• World Small Animal Veterinary Association (WSAVA). Feeding treats to your dog. Checked October 25, 2026.
• World Small Animal Veterinary Association (WSAVA). Feeding treats to your cat. Checked October 25, 2026.
• Zanghi BM, Gardner CL. Frontiers in Veterinary Science 5:317. Total Water Intake and Urine Measures of Hydration in Adult Dogs Drinking Tap Water or a Nutrient-Enriched Water (2018). Checked October 25, 2026.
• Osborne CA. dvm360. The ins and outs of polyuria and polydipsia. Checked October 25, 2026.
• Merck Veterinary Manual. Whelping and Queening in Bitches and Queens. Checked October 25, 2026.
• Musters J, de Gier J, Kooistra HS, Okkens AC. Theriogenology 75(9):1596–1601. Questionnaire-based survey of parturition in the queen (2011). Checked October 25, 2026.
• ASPCA. Cutting Pet Care Costs (2021 update) (2021). Checked October 25, 2026.
• World Small Animal Veterinary Association (WSAVA) Global Nutrition Committee. Body Condition Score charts for dogs and cats (2013). Checked October 25, 2026.
• American Animal Hospital Association (AAHA). 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats, Table 2: Summary of BCS scales and their relationship with body fat and body weight (2021). Checked October 25, 2026.
• Montoya M, Morrison JA, Arrignon F, et al. Frontiers in Veterinary Science 10:1082102. Life expectancy tables for dogs and cats derived from clinical data (Banfield Pet Hospital records, USA) (2023). Checked October 25, 2026.
• McMillan KM, Bielby J, Williams CL, et al. Scientific Reports 14:531. Longevity of companion dog breeds: those at risk from early death (Table S3, median longevity by breed) (2024). Checked October 25, 2026.
• Teng KT, Brodbelt DC, Church DB, O'Neill DG. Journal of Feline Medicine and Surgery 26(5). Life tables of annual life expectancy and risk factors for mortality in cats in the UK (VetCompass) (2024). Checked October 25, 2026.
• Hawthorne AJ, Booles D, Nugent PA, Gettinby G, Wilkinson J. The Journal of Nutrition 134(8):2027S–2030S. Body-Weight Changes during Growth in Puppies of Different Breeds (Table 1, logistic growth curves) (2004). Checked October 25, 2026.
• Merck Veterinary Manual (Sanderson SL). Feeding Practices in Small Animals. Checked October 25, 2026.
• Merck Veterinary Manual. Feeding Schedule for Puppies (table). Checked October 25, 2026.
• ASPCA (ASPCApro). Kitten Age & Weight Chart (2023). Checked October 25, 2026.
• Merck Veterinary Manual (Davidson AP). Breeding Management of Bitches. Checked October 25, 2026.
• Merck Veterinary Manual. Features of the Reproductive Cycle (table). Checked October 25, 2026.
• Cornell University College of Veterinary Medicine, Riney Canine Health Center. Dog Estrous Cycles. Checked October 25, 2026.
• American Kennel Club (AKC). How to Choose the Best Crate for Your Dog. Checked October 25, 2026.
• International Air Transport Association (IATA). Live Animals Regulations, Container Requirement 1 (cats and dogs). Checked October 25, 2026.
• American Association of Feline Practitioners (AAFP) and International Society of Feline Medicine (ISFM). Why is my cat urinating and/or defecating outside of the litter box? (client brochure, 2014 House-Soiling Guidelines) (2014). Checked October 25, 2026.
• Cornell Feline Health Center. Feline Behavior Problems: House Soiling. Checked October 25, 2026.
• Ellis SLH, Rodan I, Carney HC, et al. Journal of Feline Medicine and Surgery 15:219–230. AAFP and ISFM Feline Environmental Needs Guidelines (2013). Checked October 25, 2026.
• U.S. Food and Drug Administration (FDA), Center for Veterinary Medicine. Get the Facts! Raw Pet Food Diets can be Dangerous to You and Your Pet. Checked October 25, 2026.
• American Veterinary Medical Association (AVMA). Raw diets for dogs and cats (policy). Checked October 25, 2026.
• American Animal Hospital Association (AAHA). 2021 AAHA Nutrition and Weight Management Guidelines: Raw protein diet (2021). Checked October 25, 2026.
• Merck Veterinary Manual. Pregnancy Determination in Bitches and Queens. Checked October 25, 2026.
• Merck Veterinary Manual. Labor, Delivery, and Postpartum Care in Bitches and Queens. Checked October 25, 2026.