Sources & method

This site is run anonymously, so trust has to come from the method, not a face. Here is exactly where each number comes from — you can open every source and check it yourself.

How the numbers stay right

• Breed weights — 159 dog breeds and 11 cat breeds — come straight from Wikidata’s open (CC0) breed data, published by the Wikimedia Foundation. A robot never writes a number: an automated check re-reads Wikidata every week and fails loudly if any range has drifted. A human then reads the source and updates it by hand.
• The dog-age formula is the peer-reviewed epigenetic model of Wang et al. (2020), not the “multiply by 7” myth. It is covered by a test that checks the formula against the values published in the paper.
• The cat-age table follows International Cat Care’s published conversion. The Cornell Feline Health Center publishes a different one — a gap of 3 human years that holds constant past a cat’s second birthday — so the calculator shows both instead of picking one.
• Growth timing — that larger dog breeds take longer to reach adult weight — is from Hawthorne et al. (2004). How much a kitten weighs at each age is from DiGangi et al. (2019), a study that stops at 20 weeks and is never extrapolated past that.
• Calorie needs, for both dogs and cats, start from the same Merck Veterinary Manual formula for resting energy requirement. The cat figure is checked against a table the WSAVA Global Nutrition Committee publishes using a different formula.

The documents

• Wikidata — dog breed mass (property P2067)

  Wikimedia Foundation — query run 2026-07-22, CC0 license

• Wikidata — cat breed mass (property P2067)

  Wikimedia Foundation — query run 2026-07-28, CC0 license

• Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome

  Wang et al., Cell Systems — 2020, vol. 11, no. 2, p. 176–185.e6 (DNA methylation in 104 Labradors)

• Body-Weight Changes during Growth in Puppies of Different Breeds

  Hawthorne et al., Journal of Nutrition — 2004, vol. 134, p. 2027S

• Management of Reproduction — gestation period in the bitch

  Merck Veterinary Manual — “Approximate Gestation Periods” table, accessed 2026-07-23

• Dystocia in Small Animals

  Merck Veterinary Manual — “Diagnosis of Dystocia in Small Animals” section, accessed 2026-07-28

• Factors affecting gestation duration in the bitch

  Eilts et al., Theriogenology — 2005, vol. 64, no. 2, p. 242–251

• Nutritional Requirements of Small Animals — energy requirements of the dog and cat

  Merck Veterinary Manual — “Energy” section, accessed 2026-07-23

• Chocolate Toxicosis in Animals

  Merck Veterinary Manual — “Methylxanthine Content of Various Types of Chocolate” table and “Etiology” section, accessed 2026-07-28

• ASPCA Poison Control

  ASPCA — 24-hour emergency line, accessed 2026-07-28

• How old is your cat? — life stage and human equivalent age

  International Cat Care (Cat Friendly Clinic) — accessed 2026-07-28

• The Special Needs of the Senior Cat — cat age in human years

  Cornell Feline Health Center, Cornell University — accessed 2026-07-28 (golden-test source, not used to build the calculation)

• Calorie Needs for an Average Healthy Adult Cat in Ideal Body Condition

  WSAVA Global Nutrition Committee — updated July 2020 (golden-test source, not used to build the calculation)

• Assessment of body weight for age determination in kittens

  DiGangi et al., Journal of Feline Medicine and Surgery — 2019 (tables 1 and 2, weight-for-age, male and female)

• Kitten Age & Weight Chart

  ASPCA Pro — 2023 (golden-test source, not used to build the calculation)