Sources and methodology
How we build these calculators
- Calories: RER = 70 × (kg)0.75; daily calories = RER × the AAHA 2021 life-stage factor. Where AAHA gives a range, we show the range. Treats default to 10% (WSAVA).
- Puppy growth: logistic growth curves from Hawthorne et al. 2004 (12 breeds): share of adult weight = 1 ÷ (1 + e−k(t − x0)), k = ln 99 ÷ (T99 − x0), averaged by size class. Result ±10%.
- Dog years: the AKC dog-age chart by size (1–16 years), interpolated between whole years; plus the Wang et al. 2020 epigenetic clock, 16 × ln(age) + 31.
- Dog life stages: 2019 AAHA Canine Life Stage Guidelines; senior ages by size from the AVMA, or 75% of the AKC breed life expectancy.
- Cat years and stages: International Cat Care chart; 2021 AAHA/AAFP Feline Life Stage Guidelines.
- Pregnancy: Merck Veterinary Manual gestation lengths (58–72 days from first mating; 64–66 from the LH surge; 62–64 from ovulation; 56–58 from diestrus day 1) and dystocia signs.
- Breeds: AKC breed-standard weight, height and life expectancy for 80 breeds, copied from each AKC breed page on 20 October 2026.
We checked every number against the sources below before publishing. Nothing is invented: where we could not find a source for a figure (for example a “senior” calorie factor), we left it out. We have no vet on staff and no vet has reviewed this site; please use the results to talk to your own vet.
All sources
- AAHA. 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats, Box 1: Energy requirement calculations (RER/MER life-stage factors). www.aaha.org/wp-content/uploads/globalassets/02-guidelines/2021-nutrition-and-weight-management/resourcepdfs/nutritiongl_box1.pdf
Used on: Dog Calorie Calculator, Cat Food Calculator, Dog Pregnancy Calculator - AAHA. 2021 AAHA Nutrition and Weight Management Guidelines for Dogs and Cats. www.aaha.org/resources/2021-aaha-nutrition-and-weight-management-guidelines/
Used on: Dog Calorie Calculator, Cat Food Calculator - Merck Veterinary Manual. Nutritional Requirements of Small Animals; table: Daily maintenance energy requirements for dogs and cats. www.merckvetmanual.com/management-and-nutrition/nutrition-small-animals/nutritional-requirements-of-small-animals
Used on: Dog Calorie Calculator, Cat Food Calculator - Pet Nutrition Alliance. Calculating Calories Based on Pet Needs (RER/MER factors). petnutritionalliance.org/wp-content/uploads/2023/03/MER.RER_.PNA_.pdf
Used on: Dog Calorie Calculator, Cat Food Calculator - WSAVA Global Nutrition Committee. Global Nutrition Guidelines and toolkit (body condition score charts). wsava.org/global-guidelines/global-nutrition-guidelines/
Used on: Puppy Weight Calculator, Dog Calorie Calculator, Cat Food Calculator - WSAVA. Feeding treats to your dog (treats no more than 10% of daily calories). wsava.org/wp-content/uploads/2024/06/Feeding-treats-to-your-dog-v2.pdf
Used on: Dog Calorie Calculator - WSAVA. Feeding treats to your cat (treats no more than 10% of daily calories). wsava.org/wp-content/uploads/2024/06/Feeding-treats-to-your-cat-v2.pdf
Used on: Cat Food Calculator - Tufts Petfoodology. What Nutritionists Wish You Knew: 5 Homecooked Diet Mistakes & Misconceptions (most dry foods 300–400 kcal per cup). sites.tufts.edu/petfoodology/2023/03/31/5-homecooked-diet-mistakes-misconceptions/
Used on: Dog Calorie Calculator - Tufts Petfoodology. Should You Be Weighing Your Pet’s Food? (example cat food of 400 kcal per cup). sites.tufts.edu/petfoodology/2021/08/16/should-you-be-weighing-your-pets-food/
Used on: Cat Food Calculator - Tufts Now. Wide Variation in Calorie Content among “Low Calorie” Pet Foods (2010). now.tufts.edu/2010/01/26/wide-variation-calorie-content-among-low-calorie-pet-foods
Used on: Dog Calorie Calculator, Cat Food Calculator - Hawthorne AJ, Booles D, Nugent PA, Wilkinson J, Gettinby G. Body-weight changes during growth in puppies of different breeds. J Nutr. 2004;134(8 Suppl):2027S–2030S. doi.org/10.1093/jn/134.8.2027S
Used on: Puppy Weight Calculator, Dog Size Calculator - Salt C, Morris PJ, German AJ, Wilson D, et al. Growth standard charts for monitoring bodyweight in dogs of different sizes. PLOS ONE. 2017;12(9):e0182064. doi.org/10.1371/journal.pone.0182064
Used on: Puppy Weight Calculator, Dog Size Calculator - American Kennel Club. Dog breed pages (breed-standard height, weight and life expectancy), accessed 20 October 2026. www.akc.org/dog-breeds/
Used on: Puppy Weight Calculator, Dog Age Calculator, Dog Size Calculator - American Kennel Club. How to Calculate Dog Years to Human Years (dog age chart by size). www.akc.org/expert-advice/health/how-to-calculate-dog-years-to-human-years/
Used on: Dog Years to Human Years, Dog Age Calculator - American Veterinary Medical Association. Senior pets. www.avma.org/resources-tools/pet-owners/petcare/senior-pets
Used on: Dog Years to Human Years, Dog Age Calculator - Wang T, Ma J, Hogan AN, et al. Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome. Cell Systems. 2020;11(2):176–185. doi.org/10.1016/j.cels.2020.06.006
Used on: Dog Years to Human Years, Dog Age Calculator - UC Davis School of Veterinary Medicine. Calculating Your Dog’s Age. healthtopics.vetmed.ucdavis.edu/health-topics/canine/calculating-your-dogs-age
Used on: Dog Years to Human Years - AAHA. 2019 AAHA Canine Life Stage Guidelines: Canine life stage definitions. www.aaha.org/resources/life-stage-canine-2019/canine-life-stage-definitions/
Used on: Dog Years to Human Years, Dog Age Calculator - Quimby J, Gowland S, Carney HC, et al. 2021 AAHA/AAFP Feline Life Stage Guidelines. J Feline Med Surg. 2021;23(3):211–233. doi.org/10.1177/1098612X21993657
Used on: Cat Food Calculator, Cat Years to Human Years, Cat Age Calculator - AAHA. 2021 AAHA/AAFP Feline Life Stage Guidelines: Feline life stage definitions. www.aaha.org/resources/2021-aaha-aafp-feline-life-stage-guidelines/feline-life-stage-definitions/
Used on: Cat Years to Human Years, Cat Age Calculator - International Cat Care. How to tell your cat’s age in human years (cat age chart). icatcare.org/articles/how-to-tell-your-cats-age-in-human-years
Used on: Cat Years to Human Years, Cat Age Calculator - Cornell Feline Health Center. Obesity. www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/obesity
Used on: Cat Food Calculator - Cornell Feline Health Center. Hepatic lipidosis. www.vet.cornell.edu/departments-centers-and-institutes/cornell-feline-health-center/health-information/feline-health-topics/hepatic-lipidosis
Used on: Cat Food Calculator - Hoelmkjaer KM, Bjørnvad CR. Management of obesity in cats. Vet Med (Auckl). Research and Reports (weight-loss rate 0.5–2% per week). doi.org/10.2147/VMRR.S40869
Used on: Cat Food Calculator - Merck Veterinary Manual. Whelping and Queening in Bitches and Queens (gestation length, temperature drop). www.merckvetmanual.com/management-and-nutrition/management-of-reproduction-dogs-and-cats/whelping-and-queening-in-bitches-and-queens
Used on: Dog Pregnancy Calculator - Merck Veterinary Manual. Dystocia in Small Animals (signs of prolonged or abnormal labour). www.merckvetmanual.com/reproductive-system/reproductive-diseases-of-the-female-small-animal/dystocia-in-small-animals
Used on: Dog Pregnancy Calculator - Merck Veterinary Manual, Dog Owners. Management of Reproduction in Dogs (pregnancy tests and timing). www.merckvetmanual.com/dog-owners/reproductive-disorders-of-dogs/management-of-reproduction-in-dogs
Used on: Dog Pregnancy Calculator - American Kennel Club. The dog reproductive cycle and how long dogs are pregnant (about 63 days from ovulation). www.akc.org/expert-advice/dog-breeding/dog-reproductive-cycle/
Used on: Dog Pregnancy Calculator - Concannon PW. Reproductive cycles of the domestic bitch. Anim Reprod Sci. 2011;124(3–4):200–210. doi.org/10.1016/j.anireprosci.2010.08.028
Used on: Dog Pregnancy Calculator
Last reviewed 20 October 2026.