How to calculate dog age
Year 1 = 15 · Year 2 = +9 · Each later year = +4 to +7 by size
Worked example. Age in human years: 39 years.
Example inputs — Dog's age: 5 years; Size: Medium (21–50 lb). Starting values are illustrative.
From George Guju, founder of Calculyn · Educational calculator guidance, not professional advice.
How it works
The old "multiply by 7" rule is a myth. Dogs mature fast in their first two years (about 24 human years), then age 4–7 human years per year depending on size — bigger dogs age faster.
Assumptions & limitations
- Results are rounded for display.
Formula and assumptions reviewed October 2026 by the Calculyn team. How we build our calculators
Frequently asked questions
Is this exact?
No — it's a widely used veterinary rule of thumb. Breed and health matter too.