Dog age calculator
Enter your dog's age and size to see its rough equivalent in human years. Two methods are shown side by side: the familiar rule of thumb with 15, 9 and then a yearly amount by size, and a newer formula based on DNA methylation.
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How to use it
- Enter your dog’s age in years and months.
- Pick the size of your dog.
- Read the human age by each method.
How it works
Rule of thumb (by size). The first dog year counts as 15 human years and the second as 9, so a 2-year-old dog is 24. Each later year adds a fixed amount that grows with size: 4 for small dogs, 4.5 for medium, 5 for large and 5.5 for giant. The sizes are our adaptation of the common “15, 9, then a steady rate” guidance and are an approximation. For ages under one or two years the calculator interpolates in a straight line.
Epigenetic formula. Human age = 16 × ln(dog age) + 31, from Wang et al., Cell Systems, 2020 (Labrador retrievers). It is shown for dogs aged 3 months and over, because the logarithm gives meaningless values for very young puppies.
Worked example
A medium dog aged 5:
- rule of thumb: 24 + 3 × 4.5 = 37.5 human years
- epigenetic: 16 × ln 5 + 31 = 16 × 1.609 + 31 = 56.8 human years
Limits and tips
- Neither number is a medical measure. Breed, health and lifestyle change how a dog ages.
- For questions about your dog’s health or senior care, ask your vet.
Frequently asked questions
Is one dog year really seven human years?
No. The "multiply by 7" rule is a myth. Dogs mature very fast in the first two years, then age more slowly. Common guidance counts about 15 human years for the first dog year and 9 for the second.
What do the size categories mean?
Roughly, small dogs weigh under 20 lb (9 kg), medium dogs 20–50 lb, large dogs over 50 lb and giant breeds over about 100 lb. Larger dogs tend to age faster later in life, so each year after the second counts for more.
What is the epigenetic formula?
In 2020 Wang and colleagues compared DNA methylation in dogs and humans (Cell Systems, 2020) and proposed human age = 16 × ln(dog age) + 31. It was derived from Labrador retrievers, so it ignores breed size.
Why do the two methods give different results?
They answer different questions. The rule of thumb is simple and size-based. The epigenetic formula follows chemical changes in the DNA of one breed and puts a 5-year-old dog near 57 human years, older than the size rule does.