Where the Formulas Come From
We do not make numbers up. Every PawSums calculator uses a formula or chart from published veterinary sources, and this page names the exact source for each. Results are estimates for healthy pets and do not replace an exam by a veterinarian.
Daily calories and food portion (dog and cat)
We compute resting energy as RER = 70 x (weight in kg ^ 0.75) kcal/day,
then the daily need as MER = RER x factor based on life stage,
spay/neuter status and activity (puppy 2.5 to 3, neutered adult about 1.5,
very active 2, senior about 1.3; cat factors run lower). Your weight in
pounds is converted to kilograms before the math. The portion in cups
divides MER by the kcal/cup from your label; in kcal/100g mode it
divides by calories per 100 g and converts to ounces.
Source: NRC, Nutrient Requirements of Dogs and Cats (2006); WSAVA Global Nutrition Guidelines. The factors are mid-points of the published ranges.
Dog years to human years
We use the chart approximation: year 1 = 15 human years, year 2 = 24, then
+4 per year for a small dog (under 22 lb), +5 for a medium dog (22 to 55 lb)
and +6 for a large dog (over 55 lb). The widely shared formula
16 x ln(age) + 31 comes from an epigenetic study done only on
Labrador Retrievers, so we deliberately do not apply it to all breeds.
Source: established veterinary age charts (AVMA and related guidance on aging by breed size).
Cat years to human years
Year 1 = 15 human years, year 2 = 24, then +4 human years for every cat year. The senior stage starts around 11 cat years, geriatric past 15.
Source: the International Cat Care (iCatCare) age chart, widely used in veterinary practice.
Chocolate toxicity (theobromine)
We compute ingested theobromine from concentrations per gram: milk chocolate 2.4 mg/g, dark and semi-sweet 5.5 mg/g, unsweetened baking chocolate 16 mg/g, dry cocoa powder 26 mg/g. Ounces are converted to grams and pounds to kilograms. The dose per kg of body weight sets the level: under 20 mg/kg monitoring, 20 to 40 mg/kg mild to moderate symptoms, over 40 mg/kg an emergency vet visit. The calculator always shows a warning to contact a vet when in doubt, regardless of the result.
Source: Merck Veterinary Manual, Chocolate Toxicosis in Animals.
Daily water for a dog
Reference of 50 to 60 ml per kg of body weight per day (roughly 0.8 to 0.9 fl oz per pound) at moderate temperature and normal activity, shown in fluid ounces and cups. Sustained drinking above about 90 to 100 ml/kg (polydipsia) is an indication for a vet visit.
Source: Merck Veterinary Manual and standard veterinary hydration guidance.
Dog and cat cost of ownership
The cost calculators use no formula, just editable line items: monthly costs added directly, yearly costs spread across 12 months. The pre-filled defaults are mid-2026 US averages: wellness exams $50 to $80 and average routine visit spend of about $214 for dogs and $138 for cats (AVMA), average annual spend of about $1,533 per dog and $1,149 per cat (APPA), average accident and illness insurance premiums of $62/month for dogs and $32/month for cats (NAPHIA, 2024), and annual ranges of $1,390 to $5,295 for dogs (Rover, 2025). They are a starting point: the whole point is to replace them with your own numbers.
Source: AVMA pet ownership statistics, APPA National Pet Owners Survey, NAPHIA State of the Industry, Rover Cost of Pet Parenthood report.
What the calculators are not
The calculators produce estimates for healthy animals. They are not a veterinary diagnosis and do not account for illness, pregnancy, special diets or individual quirks. For any health question, emergency or doubt, talk to a veterinarian.
Spotted an error?
The formulas live in one file with named sources and a unit test for every value, including the pound and ounce conversions. If you think something is wrong or outdated, tell us: we fix fast.