Why "one dog year = seven human years" is wrong
Dogs mature fast early on and then age at a rate that depends heavily on size. A dog reaches roughly 15 human years by its first birthday and about 24 by its second — then adds a different number of years annually depending on whether it's a small breed or a giant one. Small dogs commonly live into their mid-teens; giant breeds often age much faster.
How this calculator works
We use the widely cited size-adjusted approach: 15 years for year one, +9 for year two, then a per-year rate of about +4 (small), +5 (medium), +6 (large), or +7 (giant) for each year after.
Frequently asked questions
Which size should I pick?
Use adult weight. If your dog is between categories, choose the one closest to its full-grown weight.
Is this exact?
No conversion is exact — it's a useful estimate. Breed, genetics, and care all affect how a dog ages.