How dog age calculator works
The "multiply by 7" rule is folklore, and it fails at both ends of the size spectrum. Vets use size-class curves instead: every dog reaches roughly 15 human years by its first birthday and 24 by its second — puppies mature extremely fast — but after that the curves separate. A small dog adds about 4 human years per dog year, a medium dog about 5, a large dog about 6, and a giant breed about 7. The calculator applies the right curve for the size class you pick.
Enter the age in years and months (the months matter for young dogs, where three months changes the answer noticeably) and choose the size class by adult weight: small up to 9 kg (20 lb), medium 9–23 kg (20–50 lb), large 23–45 kg (50–100 lb), giant over 45 kg (100 lb). The result shows the human-equivalent age, the life stage (puppy, junior, adult, senior), how many years until senior status for that size, and the typical lifespan range so you can see where your dog sits on the curve.
The result also shows what the ×7 myth would have said and how far off it is. For a 5-year-old small dog the myth says 35 human years; the size-class curve says 36 — close. For a 5-year-old Great Dane the myth says 35; the curve says 43, because giant breeds age fastest and have the shortest lives. Everything runs in your browser; nothing about your dog is sent anywhere.