Methodology

Editorial principles

• Answer first. Each page opens with a plain-language answer, then shows the work.
• Cite primary guidance. Prefer WSAVA, AAHA, AAFP, AAFCO, the National Research Council, the ASPCA, Pet Poison Helpline, and the Merck / MSD Veterinary Manual over blogs and forums.
• Show limits. Estimates are ranges where the science supports a range; every page carries a disclaimer.
• No paid placement. Brands cannot pay for a calculation, a ranking, or a recommendation.
• Dates only change when content changes. “Last reviewed” / dateModified move only when the formula, sources, or text actually change — not to look fresh.
• No invented reviewers. A “reviewed by” credit appears only when a real, named veterinarian has reviewed that page. Until then, pages cite sources and link here. See the editorial policy and About.

How drafts are made (AI disclosure)

Drafts may be written with AI assistance. Every formula, constant, threshold and reference is checked by Hammad Iqbal against the sources listed on each page before publish. AI is not treated as a veterinary authority.

Units

All internal math uses kilograms, grams, millilitres, and kilocalories. Pounds are converted with 1 lb = 0.45359237 kg, ounces with 1 oz = 28.3495 g, and results are displayed in the unit you choose with the other unit in parentheses. Rounding happens only at display time.

Energy needs: RER and MER

The dog and cat food, puppy food, and related tools start with resting energy requirement (RER), the energy a healthy animal uses at rest in a thermoneutral environment:

RER (kcal/day) = 70 × (body weight in kg)^0.75

Maintenance energy requirement (MER) multiplies RER by a factor for life stage and activity. Factors are taught in veterinary nutrition and align with ranges in the NRC Nutrient Requirements of Dogs and Cats and the WSAVA Global Nutrition Guidelines. They are starting points, because individual animals vary by 20 percent or more.

Dog factors

Cat factors

Cups per day are daily kilocalories divided by the kilocalories per cup printed on the food label (or by the kcal per 100 g, scaled, for grams). Always use the label value for your specific food, because dry foods range from roughly 280 to over 500 kcal per cup.

Puppy weight prediction

For puppies up to 16 weeks old the early-puppy rule is used:

Estimated adult weight = (current weight ÷ age in weeks) × 52

For older puppies, current weight is divided by the share of adult weight typically reached at that age, from a curve of the form 1 − e^{−3.2 × (age ÷ maturity age)}, where maturity age comes from the breed or size class (10 months for toy breeds, up to 24 months for giant breeds). The raw estimate is blended 65:35 with the midpoint of the breed or size adult range, and the displayed range is widened to at least 12 percent of the estimate. Breed ranges are averages for mixed sexes; individuals differ.

Dog age in human years

The old rule of seven human years per dog year is not used. The size-aware model counts the first year as 15 human years and the second as 9 more, then adds 4 (toy and small), 5 (medium), 6 (large), or 7 (giant) human years per dog year. Life stage labels follow the age bands in the AAHA Canine Life Stage Guidelines, with the senior threshold earlier for larger dogs (6 years for giant breeds up to 10 for small ones). An optional logarithmic curve, human age ≈ 16 × ln(dog age) + 31, is shown for comparison. It comes from Wang et al. (2020), Cell Systems, an epigenetic-clock study of 104 Labrador Retrievers (not a larger “~300” figure sometimes repeated online). It is illustrative, single-breed, and not a clinical standard.

Cat age in human years

Cats use 15 human years for the first year, 9 more for the second, and 4 for each year after. Life stages are kitten (under 6 months), junior (to 1 year), prime or adult (to 7), mature (to 11), senior (to 15), and geriatric (15 and over), based on the AAHA/AAFP Feline Life Stage Guidelines.

Homemade and raw portions

Portion ranges are shown as a percentage of body weight per day, as fed: 2 to 3 percent for adult maintenance, 2.5 to 5 percent for puppies, 3 to 4 percent for active dogs, and 1.5 to 2 percent for supervised weight loss. These are rules of thumb used in practice, not a recipe. Complete and balanced homemade diets require formulation by a veterinary nutritionist, as the WSAVA guidelines stress.

Dog body condition

The body condition helper divides weight in kilograms by height at the withers in metres squared, which is a BMI-style index. Dogs do not have a validated BMI, so the index is a rough screen. The hands-on 1 to 9 body condition score from the WSAVA Global Nutrition Committee is the clinical standard, and it takes precedence when the two disagree.

Pregnancy due date

The due date is 63 days after the start date entered. Gestation is about 63 days from ovulation, so an ovulation date gives a window of plus or minus 2 days, and a mating date gives a wider window of plus or minus 5 days, because mating can occur several days before or after ovulation. Progesterone testing and ultrasound by a veterinarian are more accurate.

Chocolate toxicity

Theobromine content per gram of chocolate is approximated from published ranges, multiplied by the amount eaten, and divided by the dog's body weight to give a dose in mg per kg.

Doses under 20 mg/kg fall in the lower band, 20 to 40 mg/kg in the mild band, 40 to 60 mg/kg in the moderate band, and above 60 mg/kg in the high band. Real products vary widely, so the tool is a triage aid. Contact a veterinarian or poison hotline whenever a dog has eaten chocolate, especially dark chocolate, baking chocolate, or a small dog.

Daily water intake

Healthy adult dogs typically drink about 50 to 60 ml per kg per day. The calculator raises the range to 60 to 80 for active dogs, 70 to 100 in hot weather, and 80 to 120 ml per kg for nursing dogs. One cup is counted as 240 ml. Wet diets supply part of the water, so dogs on them may drink less. Sudden changes are a reason to call a vet.

Known limitations

• Calculators estimate population averages, not an individual animal's needs.
• They do not account for disease, medication, pregnancy (except where stated), or breed-specific metabolism.
• Food labels and chocolate products vary, and the tool cannot read your specific label.
• Nothing here diagnoses a condition or replaces a veterinary exam.

Reporting an error

If you believe a formula or constant is wrong, send the page and a source through the contact page. Reports are checked against the cited guideline; the page date changes only when a real fix ships.

Correction log & changelog