This page covers, specifically for this site, how the age, dog age, and puppy weight calculators get their math right, how often that gets checked, and what happens when a reader finds something wrong.
How the calculators are built
All three calculators run on the browser's built-in Date object rather than a custom date library, which keeps the math consistent with how JavaScript itself defines a calendar day. The age calculator counts whole years, then whole months, then leftover days, the same order a person would use counting by hand. Before a change ships, we run it against a fixed set of worked examples, including known edge cases like a February 29 birthdate and month-end dates where the day count would otherwise go negative, and compare the output to a hand-calculated answer.
Where the dog age and puppy weight formulas come from
The dog age calculator uses the size-based aging scale published by the American Veterinary Medical Association rather than the old flat "multiply by seven" rule, because the AVMA's own guidance is explicit that dogs of different adult sizes age at different rates. The puppy weight calculator applies a growth-percentage method, the idea that a puppy of a given size class reaches a predictable share of its adult weight by 8 weeks, drawn from figures used by veterinarians and breeders rather than a formula we invented ourselves. Neither tool replaces a veterinarian who has actually examined the animal.
Update cadence
We recheck the calculators when a major browser changes how it handles date calculations, when the AVMA or comparable veterinary sources update their published guidance, or when a reader flags an edge case we had not tested. The Age Calculation Reference page carries the worked examples and the underlying CSV, and its date changes whenever the underlying figures do, not on a fixed schedule.
Who writes what
Marcus Vance writes and maintains the guides and reference content on this site; his background is on the authors page. I do not write the calculator guides myself. My role is reviewing new pages before they publish, setting the sourcing rules above, and handling corrections personally.
Corrections
If a result looks wrong, especially an edge case around leap years or breed-size bands, use the contact page. I read every correction request myself. Confirmed errors get fixed, and the reference page's date is updated to reflect it; we do not quietly change a calculator without noting that it happened.
What we will not do
We will not let a pricing arrangement or a partner change what a calculator outputs, and we will not present sponsored content as an independent guide without saying so.