Case 1
- Dog's age
- 5
- Size band
- Medium — 10 to 22 kg
39.0
Open with these valuesDog Age Calculator
39.0human years
Result: 39.0 human yearsA dog's first year counts as 15 human years and the second adds 9 more, reaching 24 by its second birthday whatever its size. After that size decides the pace: about 4 human years per year for a small dog, 5 for medium, 6 for large and 7 for giant breeds.
Worked examples
Case 2
- Dog's age
- 10
- Size band
- Large — 23 to 40 kg
72.0
Open with these valuesCase 3
- Dog's age
- 0.5
- Size band
- Small — up to 9 kg
7.5
Open with these valuesHow it's calculated
1st year = 15, 2nd year = +9, then +4 to +7 by size
- StepEnter your dog's age in years; decimals are fine for a puppy.
- StepPick the size band by adult weight — the bands are broad averages.
- ResultThe first two years count the same for every dog; only later years differ.
What this number means
The first two years are the same for every dog
Fifteen human years for the first, nine more for the second, so every dog reaches about 24 by its second birthday. Size only starts to matter from the third year on.
Times seven misses by a whole size band
At ten calendar years the curve gives 56 for a small dog and 80 for a giant breed — 24 human years apart. A single multiplier cannot hold both ends.
Pick the band by adult weight
The bands run up to 9 kg, 10 to 22 kg, 23 to 40 kg and over 40 kg. If your dog sits between two, run both and read the answer as a range.
Only the medium pace is published
The 15, the plus 9 and the further 5 per year for a medium dog come from the veterinary guidance cited here. The 4, 6 and 7 for the other bands are the common rule of thumb, and no single conversion formula is scientifically agreed on.
Commonly misread
One dog year equals seven human years.
The first year alone is about 15, and the rule ignores size entirely. After year two a giant breed gains seven human years a year while a small dog gains four.
A ten-year-old dog is a senior whatever its breed.
At ten a small dog is around 56 in human terms and a giant breed around 80. Large breeds reach that stage years earlier.
The size band changes a puppy's result.
It does not — before the third year every dog follows the same curve. A six-month puppy is 7.5 human years in every band.
Reference table
| Dog years | Small | Medium | Large | Giant |
|---|---|---|---|---|
| 1 | 15 | 15 | 15 | 15 |
| 2 | 24 | 24 | 24 | 24 |
| 5 | 36 | 39 | 42 | 45 |
| 10 | 56 | 64 | 72 | 80 |
| 15 | 76 | 89 | 102 | 115 |
Questions
How old is my dog in human years?
It depends on age and on size. Every dog is about 24 by its second birthday; after that a small dog adds roughly 4 human years per year, a medium 5, a large 6 and a giant breed 7.
Is one dog year really seven human years?
No, the times-seven rule is a myth. The first year alone is closer to 15 human years, and the rule ignores size completely, which is the single biggest factor after year two. A size-aware curve like this one describes real ageing far better.
Why does size change the result?
Larger dogs age faster once they are grown, so each calendar year buys them more human years. That is also why giant breeds count as seniors earlier and generally live shorter lives than small dogs of the same calendar age.
Can I calculate a puppy's age?
Yes. The first year is spread evenly across the twelve months, so 0.5 gives roughly 7.5 human years for a six-month-old puppy. Size makes no difference before the third year.
How well sourced are these numbers?
The first year at 15, the second at plus 9 and a further 5 per year for a medium dog come straight from the veterinary guidance this page cites. The 4, 6 and 7 for small, large and giant breeds are the widely used rule of thumb rather than a published figure, and no single conversion formula is scientifically agreed on. Read the result as a life-stage guide, not a measurement.
Sources and last check
Information, not professional advice.