What the Dog Age Calculator does
This calculator converts your dog's age into human years two ways - with the size-based chart vets and kennel clubs publish, and with the 2020 epigenetic-clock formula from DNA research - and tells you which life stage your dog is in now. Enter the age in years and months, pick small, medium, large or giant (or type the adult weight), and the answer appears at once.
The old rule of multiplying by seven is wrong at both ends: a one-year-old dog is already physically an adolescent, while small dogs age more slowly than large ones in later life. Both methods here account for that, and the page shows where they agree and where they do not.
How to use it
- Enter the age in years and months. For a puppy, put 0 years and the number of months.
- Choose the size your dog is, or will be, when fully grown: small up to 20 lb (9 kg), medium 21-50 lb, large 51-100 lb, giant over 100 lb (45 kg). Typing the adult weight picks the class for you.
- Read the chart answer in the big panel and the epigenetic answer beside it, then the life stage. If you know your breed's typical lifespan, enter it under "Typical lifespan" to move the senior threshold.
- Open the full age chart for every year from 1 to 16, or look at the line chart to see how the size chart, the DNA formula and the times-seven rule pull apart.
Reading the results
The size chart says the first two years count for about 24 human years for most dogs, after which each year adds about 4 (small) to 7 (giant) years. That is a rule of thumb distilled from veterinary experience, not a measurement - treat the answer as "about".
The epigenetic formula comes from measuring chemical marks on DNA that change with age, in dogs and in people, and matching the two. It ages young dogs very fast (a two-year-old comes out around 42) and slows down later. It was fitted on Labrador retrievers, so it fits large dogs better than toy breeds.
The life stage matters more than the number. Vets plan check-ups by stage: puppy until rapid growth stops, young adult until about 3-4 years, mature adult, then senior for the last quarter of the expected lifespan - about 9.5 years for a small dog, 7 for a giant one.
Worked example: a five-year-old beagle and a ten-year-old Labrador
A beagle weighs about 20-30 lb, so it is a medium dog. At 5 the chart reads 36 human years. The epigenetic formula gives 16 x ln(5) + 31 = 16 x 1.609 + 31 = 56.8, about 57 - well above the chart, as it typically is for middle-aged dogs. Times seven would say 35.
A Labrador is large (55-80 lb). At 10 the chart reads 66 and the formula 16 x ln(10) + 31 = 67.8: here the two agree. With a typical large-dog lifespan of 11.9 years, senior starts at 0.75 x 11.9 = 8.9 years, so a ten-year-old Labrador is a senior.
Formulas and scoring rules
- Size chart
human age = chart value for the size class at the dog's ageBetween whole years the chart is interpolated in a straight line; under one year it runs from 0 at birth to the one-year value; after 16 it continues the last yearly step. Those three cases are labelled on the page.- Epigenetic clock (Wang et al., 2020)
human age = 16 x ln(dog age in years) + 31Natural logarithm. Withheld under 3 months, where it falls towards zero and then below it; less reliable in the first year.- Senior threshold (AAHA 2019)
senior from = 0.75 x expected lifespanDefault lifespans are UK median survival by size: small 12.7, medium 12.5, large 11.9 years (McMillan et al., 2024); giant 9 years from the Mastiff and St Bernard medians in the same study.
Limitations: what the result does not prove
- Both conversions are estimates for curiosity and conversation. Neither tells you how healthy your dog is, and neither replaces a check-up - this is not veterinary advice.
- Breeds differ within a size class. Flat-faced breeds and some large breeds have shorter lives than their size suggests; many small terriers live longer. Use the lifespan field if you know your breed's figure.
- The epigenetic formula comes from one study of 104 Labradors and is least reliable for puppies and for breeds unlike Labradors.
- Mixed-breed dogs should use the size they are as adults; a puppy's current weight will put it in too small a class.
Privacy: where your data goes
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Standards and sources
- Wang T. et al. (2020) Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylation landscape, Cell Systems
- American Kennel Club - How to calculate dog years to human years
- 2019 AAHA Canine Life Stage Guidelines
- McMillan K.M. et al. (2024) Longevity of companion dog breeds: those at risk from early death, Scientific Reports
Frequently asked questions
How old is my dog in human years?
Enter the age and size above. As a rough guide from the size chart, a one-year-old is about 15, a two-year-old about 24, and each year after adds about 4 for small dogs, 5 for medium, 6 for large and 7 or more for giant breeds.
Is one dog year really seven human years?
No. Dogs mature far faster than that at first - a one-year-old is already about 15 by the chart - and the pace then slows, at a rate that depends on size. Times seven underestimates young dogs and overestimates old small dogs.
Do small dogs age slower than big dogs?
In later life, yes. The first two years are similar, but after that large and giant dogs age faster and live shorter lives on average: in a 2024 UK study small breeds had a median lifespan of 12.7 years and large breeds 11.9.
What is the epigenetic dog age formula?
Human age = 16 x ln(dog age) + 31, from a 2020 study in Cell Systems that compared age-related DNA methylation in Labrador retrievers and people. It ages dogs very quickly early on: a one-year-old maps to 31, a four-year-old to about 53.
When is a dog considered a senior?
Veterinary guidelines (AAHA 2019) define a senior as a dog in the last 25% of its expected lifespan. For a typical small dog that is from about 9.5 years; for a large dog about 9; for a giant breed about 7.
How do I work out a puppy's age in human years?
Enter 0 years and the age in months. The chart has no rows under a year, so the page draws a straight line from birth to the one-year value and says so; the epigenetic formula is not shown under three months, where it stops making sense.
Which size is my mixed-breed dog?
Go by adult weight: up to 20 lb (9 kg) small, 21-50 lb (about 9.5-23 kg) medium, 51-100 lb (23-45 kg) large, and over 100 lb giant. Type the weight in kilograms or pounds and the size class is chosen for you.
Last reviewed by the A2Z.Tools team against the sources listed above.
