Dog Age Calculator
A 5-year-old medium dog is about 39 human years, not the 35 the old multiply-by-7 rule suggests. This dog age calculator converts your dog's age into human years using a size-adjusted method. Enter your dog's age in years and pick a breed size to see an estimated human age and life stage.
Quick answer
The first year of a dog's life counts for about 15 human years.
What this tells you
- •The first year of a dog's life counts for about 15 human years.
- •The second year adds roughly 9 more human years, reaching about 24.
- •After age two, each dog year adds 4 to 6 human years depending on breed size.
- •Larger dogs age faster, so size changes the result for dogs older than two.
How to Use
- 1Enter your dog's age in years. You can use decimals such as 0.5 for a six-month puppy.
- 2Choose a breed size: small, medium, or large.
- 3Click Calculate to see the estimated age in human years and the life stage.
How It Works
Formula
Year 1: human = 15 x dog age. Up to year 2: human = 15 + (dog age - 1) x 9. After year 2: human = 24 + (dog age - 2) x perYear, where perYear = 4 (small), 5 (medium), or 6 (large).Dogs mature fast early in life, so the first year is worth about 15 human years and the second adds about 9 more for a running total near 24. From age two onward, aging slows but depends on size. Small breeds add about 4 human years per dog year, medium breeds about 5, and large breeds about 6 because larger dogs tend to have shorter lifespans.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
5-year-old medium dog
The first two years count as 24 human years. The next three years add 3 x 5 = 15, giving 24 + 15 = 39 human years.
5-year-old large dog
Same age as the medium dog, but large breeds add 6 human years per dog year after age two. That gives 24 + 3 x 6 = 42 human years, which shows why size matters.
Dog Age in Human Years by Size
Estimated human age for common dog ages across small, medium, and large breeds.
| Dog age (years) | Small breed | Medium breed | Large breed |
|---|---|---|---|
| 1 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 |
| 3 | 28 | 29 | 30 |
| 5 | 36 | 39 | 42 |
| 7 | 44 | 49 | 54 |
| 10 | 56 | 64 | 72 |
Values are estimates and round to the nearest human year for easy comparison.
Common mistakes
- Using the flat multiply-by-7 myth, which overstates early aging and ignores how dogs mature.
- Ignoring breed size, even though large dogs age faster than small dogs after the first two years.
- Applying adult aging rates to the first two years, when puppies actually age much faster early on.