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About this tool
See your dog or cat's age in human years with vet-style size-based math, life stages, and lifespan progress.
The Pet Age Calculator converts a dog's or cat's age into human years using the vet-style staged rule rather than the old 'multiply by seven' shortcut: the first year counts as 15 human years, the second adds 9 more, and every year after that adds a fixed amount set by species and body size. For dogs that yearly rate is +4 for small breeds under 10 kg, +5 for medium (10–25 kg), +6 for large (25–45 kg) and +7 for giant breeds over 45 kg; cats add +4 a year. You get the human-year equivalent, the life stage from puppy or kitten through geriatric, and how far along a typical lifespan your pet is — and it converts back the other way too.
Open Pet Age Calculator (Dog & Cat Years) on AltFTool — it loads instantly in your browser.
Pick Dog or Cat, then choose a dog size band from Small under 10 kg to Giant over 45 kg.
Use "Enter age" with the Years and Months sliders, or switch to "Pick birthday" to have the age computed for you.
Read the human-year figure, the life stage from Puppy to Geriatric and the lifespan progress, then press Copy result.
A 10-year-old Chihuahua and a 10-year-old mastiff get different answers because the per-year rate changes with body size, from +4 up to +7.
Each result lands on a stage band — Puppy, Junior, Adult, Mature, Senior, Geriatric — with the exact year boundaries for that size, which is what actually drives diet and screening decisions.
Enter a human age instead and it inverts the same formula to tell you what that is in dog or cat years, and a birthday field fills in the age down to the month.
Count the first year as 15 human years, the second year as 9 more (so a 2-year-old dog is about 24), then add 4 to 7 human years for every year after that depending on size — +4 small, +5 medium, +6 large, +7 giant. A 5-year-old medium dog therefore works out to roughly 39 human years.
Yes, it is a rough average that misreads both ends of life. Dogs reach the equivalent of human adolescence inside their first year, which is why year one counts as about 15, and large breeds then age faster per year than small ones — a flat multiplier of 7 cannot capture either effect.
Cats follow the same 15-then-9 opening but add a steady 4 human years annually from year three, regardless of size, with a typical lifespan of 12–18 years. That makes a 15-year-old cat about 76 in human terms and puts it at the start of the geriatric stage.
It depends on size: small dogs enter the senior band at about 10 years, medium at 9, large at 8 and giant breeds at 7, while cats are treated as senior from around 11. These are general planning guidelines — your vet sets the actual screening schedule based on breed, weight and health history.
Add the Pet Age Calculator (Dog & Cat Years) widget to your blog or website — free, responsive, no signup. Just keep the “Widget by AltFTool” credit link visible.
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