Dog Age Calculator
Enter your dog’s age to see the rough equivalent in human years. It uses the common rule of thumb in which the first two years count for much more than later years, not a flat multiply by 7.
Last updated October 20, 2026
Use decimals for months, e.g. 1.5
Result
39 human years
A 5-year-old dog is about 39 in human years.
| Rule | Human years |
|---|---|
| This rule | 39 |
| Multiply by 7 | 35 |
A rule of thumb for a medium-sized dog. Size, breed and health change how a dog ages.
Show the work
Formula: Up to 1 year: 15 x age. Between 1 and 2 years: 15 + 9 x (age - 1). Over 2 years: 24 + 5 x (age - 2).
- Dog age entered: 5 years.
- Age is over 2 years: 24 + 5 x (5 - 2) = 39.
- For comparison, the multiply-by-7 rule: 5 x 7 = 35.
Result: 39 human years
How dog years are converted
age 1 = 15
age 2 = 24
after that, add 5 human years for every dog year
The first year of a dog’s life counts as about 15 human years and the second year adds about 9 more, so a 2-year-old dog is about 24 in human terms. Each year after that adds about 5. A 5-year-old dog is 24 + 3 × 5 = 39. Ages between whole years are worked out in a straight line.
The simple multiply-by-7 rule is not accurate: it makes a 1-year-old dog 7, when a dog that age is already fully grown. This rule of thumb is for a medium-sized dog. Larger dogs tend to age faster and smaller dogs more slowly, and published charts by size disagree on the exact numbers, so this page does not use one.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Also useful alongside this calculator: Age Calculator, Date Difference Calculator and Weeks Between Dates.
Puppies and part-years
Ages are not limited to whole years. In the first year the calculator counts 15 human years for each dog year, so a dog of 6 months (0.5) is 7.5 and a dog of 8 months (about 0.67) is 10. Between 1 and 2 years it adds 9 human years per dog year, so 18 months (1.5) is 15 + 4.5 = 19.5.
After the second birthday each extra dog year is 5 human years, so a 2.5-year-old dog is 24 + 2.5 = 26.5. Ages up to 30 years are accepted. Enter months as a fraction of a year: divide the number of months by 12.
Where the multiply-by-7 rule goes wrong
The 7-to-1 rule gives a straight line, but the rule of thumb on this page does not. The two give the same answer at only one age, 7 years, where both say 49. Before that the old rule understates young dogs: at 1 year it says 7 against 15, and at 3 years it says 21 against 29.
After 7 years the old rule overstates older dogs. A 10-year-old dog is 64 by this rule and 70 by the old one, and a 15-year-old dog is 89 against 105. The gap grows every year, which is why a flat multiplier is a poor guide to a dog’s life stage.
What the research says
A 2020 study from the University of California San Diego looked at DNA methylation in 105 Labrador retrievers. It found that dog aging is not a straight line against human aging, and estimated that a one-year-old dog is similar to a 30-year-old human and a four-year-old dog to a 52-year-old human. These research-based estimates are higher in the early years than the rule of thumb on this page and were measured in one breed, so use both as rough guides.
How to use the Dog Age Calculator
- Enter your dog’s age in years, with decimals for months (for example 1.5).
- Read the age in human years and compare it with the multiply-by-7 rule.
- Use Copy, Print or Share to keep the result.
Worked example
A 5-year-old dog is 15 for the first year, 9 for the second and 5 for each of the next 3 years: 15 + 9 + 15 = 39 human years. The multiply-by-7 rule would say 35. For a dog of 2 years and 6 months, the first two years are worth 24 and the extra half year adds 0.5 × 5 = 2.5, so the answer is 26.5.
| Dog age | Human years (this rule) | Multiply by 7 |
|---|---|---|
| 1 | 15 | 7 |
| 2 | 24 | 14 |
| 3 | 29 | 21 |
| 5 | 39 | 35 |
| 7 | 49 | 49 |
| 10 | 64 | 70 |
| 12 | 74 | 84 |
| 15 | 89 | 105 |
Frequently asked questions
How old is a 1-year-old dog in human years?
About 15 by the common rule of thumb. Research on Labradors suggests it is closer to 30.
Is one dog year really seven human years?
No. Dogs mature much faster in their first two years and then age more slowly than 7 to 1.
Do big dogs age faster than small dogs?
Larger dogs tend to have shorter lifespans, so they are often described as aging faster. This calculator uses one rule for all sizes and is only an estimate.
Can I enter months, and how old is a 10-year-old dog?
Yes. Use decimals: 18 months is 1.5 years, which is 19.5 human years by this rule. A 10-year-old dog is 24 + 8 × 5 = 64 human years.
Is this a medical or veterinary tool, and are my numbers stored?
No. It is a rough guide for curiosity, not veterinary advice, so ask your vet about your own dog’s health and care. The calculation runs in your browser and nothing you enter is saved or uploaded.