Dog Age Calculator
The old 'multiply by 7' rule is rough. This uses a common size-based approximation that better reflects different aging rates.
| Dog age | years |
| Dog size |
Result
Your result will appear here.
How it works
Dogs mature quickly in their first two years, then age at different rates depending on size. Smaller dogs tend to live longer and age slower in later years than giant breeds.
Formula
Year 1: ~15 human years; year 2: adds ~9 (24 total); each additional year adds ~4 (small), ~5 (medium), ~6 (large), or ~7 (giant) human years.
Worked example
A 5-year-old medium dog: first two years give 24, plus 3 extra years × 5 = +15, for ~39 human years equivalent.
Assumptions
This is an approximation based on common guidelines, not a biological law. Individual dogs vary by breed, genetics, diet and healthcare.
Reading the result
Use it as a rough guide to life stage (puppy/adult/senior), not as a precise measure.
For general information only.
How to use the Dog Age Calculator
It takes a few seconds, and every figure is calculated in your browser.
- Enter your dog's age.
- Pick your dog's size.
- Press Calculate — the result appears in the dark panel beside the form.
- Use Copy, CSV, Share or Print under the result if you want to keep it.
Dog Age Calculator — frequently asked questions
What formula does the Dog Age Calculator use?
Year 1: ~15 human years; year 2: adds ~9 (24 total); each additional year adds ~4 (small), ~5 (medium), ~6 (large), or ~7 (giant) human years.
How does the Dog Age Calculator work?
Dogs mature quickly in their first two years, then age at different rates depending on size. Smaller dogs tend to live longer and age slower in later years than giant breeds.
What assumptions and limitations should I know about?
This is an approximation based on common guidelines, not a biological law. Individual dogs vary by breed, genetics, diet and healthcare.
Can you walk through a worked example?
A 5-year-old medium dog: first two years give 24, plus 3 extra years × 5 = +15, for ~39 human years equivalent.
Last updated 10 November 2026 · Formula, worked example and assumptions are documented above, and every result is calculated in your browser.