Pet Owner Tools
Math for people who love pets.
Free calculators for dog, cat, rabbit, and fish owners — lifetime cost, insurance break-even, puppy growth prediction, age in human years, food portion, tank care. Every tool runs 100% in your browser; no signup.
Cost + planning
Pet Lifetime Cost Calculator
Estimate total cost of ownership over your pet's expected lifespan — food, vet, insurance, gear.
Pet Insurance Break-Even Calculator
How much you have to pay in vet bills for insurance premiums to have been worth it.
Puppy Adult Weight Predictor
Estimate a puppy's adult weight from its current weight and age.
Everyday pet-owner calculators
Dog Age in Human Years
Non-linear formula based on breed size — more accurate than the '×7' rule.
Cat Age in Human Years
Cats age faster their first 2 years, then ~4 human years per cat year.
Universal Pet Age
Approximate human-equivalent age for dogs, cats, rabbits, and more.
Pet Food Portion
Daily calorie and portion size by pet weight, activity level, life stage.
Fish Tank Stocking
Recommended fish load for your tank size and species mix.
Aquarium Water Change
Recommended weekly water change volume + schedule for a healthy tank.
Before you commit to a pet
Most people vastly underestimate the total cost of pet ownership. Adoption fees are the smallest line item; food, insurance, and unexpected vet care dominate a pet's lifetime cost. Run Pet Lifetime Cost before adopting to see the honest 10-15 year number. Then, once you have or are getting a pet, Pet Insurance Break-Even answers the big financial question: does insurance actually pay off, or would that money be better held in a dedicated vet-emergency savings account? For most healthy young pets, self-insurance wins mathematically; for large breeds and predisposed-condition breeds, insurance is the safer bet.
Aging + growth
The old "1 pet year = 7 human years" rule is inaccurate; pets age faster in their first two years and then more slowly. Our Dog Age and Cat Age calculators use the current AVMA/veterinary formulas which account for breed size (large breeds age faster than small) and the front-loaded aging curve. For a young puppy, Puppy Adult Weight Predictor projects the adult size — useful when picking crate size, harness size, and preparing for how much food a 60-lb adult vs 12-lb adult will need.
Everyday care
Pet Food Portion computes daily calorie needs (RER × activity multiplier) and translates that into cups or grams of food based on your bag's calorie density. Under-feeding and over-feeding are equally common; a scale is more reliable than a scoop for larger dogs. For aquarium keepers, Fish Tank Stocking uses the "1 inch of fish per gallon" rule adjusted for schooling behavior and territorial species, and Aquarium Water Change gives the weekly volume needed to keep nitrates below stress-inducing levels.
Not veterinary advice
These calculators use general formulas from standard veterinary and industry references. They do not diagnose, dose medication, or replace an in-person exam. Any weight loss, behavior change, or new symptom warrants a call to your veterinarian. Feed amounts, growth curves, and insurance value all depend on your individual pet.
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