Dog Age Calculator
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Turn your dog's age in years, months or weeks into human years by breed size, with the 2020 research formula alongside.
Quick answer: a 5-year-old large dog is about 39 in human years on the size-adjusted chart (15, then +9, then +5 a year) and 57 on the 2020 UC San Diego formula, 16 × ln(5) + 31. This dog age calculator takes years, months or weeks and a size class, so a 4-month puppy and a 12-year-old Labrador both work.
📐 Formula
Size chart: 15 human years at 1 year, 24 at 2 years, then 24 + p × (age − 2), where p is 4 for small and medium dogs, 5 for large and 6 for giant. Research formula: 16 × ln(age in years) + 31, used from 8 weeks. Months and weeks are converted to years first (months ÷ 12, weeks ÷ 52.18), and the first two years of the chart are filled in a straight line.
How to use the dog age calculator
Enter your dog's age
Type the age and choose Years, Months or Weeks. Decimals such as 2.5 work, and the box accepts up to 20 years.
Pick the size class and lifespan
Choose the class that matches your dog's adult weight: small up to 20 lb (9 kg), medium 21 to 50 lb, large 51 to 100 lb or giant over 100 lb. If you know your dog's expected lifespan, enter it too.
Read both results
The main figure is the size-adjusted chart. The research formula appears beside it, so you can see where the two models agree and where they split.
Check the life stage
The label shows a life stage based on the AAHA stages: puppy, young adult, mature adult or senior, with a transitional label near the boundaries. Treat it as a prompt to talk to your vet, not as a diagnosis.
How do you convert dog years to human years?
Skip the old "multiply by 7" rule and use a curve. Dogs mature far faster than people in their first two years, then age at a pace that depends on size. The size-adjusted chart on this page counts year one as 15 human years, adds 9 for year two (24 in total), then adds 4 human years per dog year for small and medium dogs, 5 for large dogs and 6 for giant breeds.
The second figure on the calculator comes from research rather than a chart. In 2020 a team at the University of California San Diego compared DNA methylation in 104 Labrador retrievers, from puppies to 16-year-olds, with 320 people aged 1 to 103. Their formula is human age = 16 × ln(dog age) + 31, and the paper describes the match as an 8-week-old puppy at about the age of a 9-month-old baby and a 12-year-old Labrador at about 70.
Dog years to human years chart: both methods side by side
The table shows the size chart for each class and the research formula for comparison. The research column has no size input, so it is the same for every dog.
| Dog age | Small | Medium | Large | Giant | Research formula |
|---|---|---|---|---|---|
| 1 year | 15 | 15 | 15 | 15 | 31 |
| 2 years | 24 | 24 | 24 | 24 | 42 |
| 3 years | 28 | 28 | 29 | 30 | 49 |
| 5 years | 36 | 36 | 39 | 42 | 57 |
| 7 years | 44 | 44 | 49 | 54 | 62 |
| 10 years | 56 | 56 | 64 | 72 | 68 |
| 12 years | 64 | 64 | 74 | 84 | 71 |
| 15 years | 76 | 76 | 89 | 102 | 74 |
Why the two methods disagree
The two methods split from the first year: the chart says a 1-year-old dog is 15 and the formula says 31, and the gap peaks at about 21 human years between ages 3 and 5 for a small or medium dog. The formula tracks how DNA methylation changes, which is a biological measure, so a young dog scores older than the "teenager" the chart implies. The formula also comes from one breed, and the chart adds size on top of a simple pattern, so neither is a measured answer for your dog.
By age 10 giant breeds pass the formula, with the chart at 72 against 68, while small and medium dogs stay below it at 56. Large dogs pass it at about age 12. Use the chart to compare your dog with others of its size, and use the formula as a reminder of how fast dogs age early on.
Worked example: a 5-year-old large dog
A large dog (51 to 100 lb) that is 5 years old is 24 human years at its second birthday on the chart. Three more years at 5 each makes 24 + (5 × 3) = 39. The research formula gives 16 × ln(5) + 31 = 16 × 1.609 + 31, which is about 57. A small dog of the same age comes out at 24 + (4 × 3) = 36 on the chart.
Dog age in months and weeks
Puppy owners usually search for a dog age calculator in months or weeks, so the calculator accepts both. The size chart fills the first year in a straight line, so a 6-month-old puppy is 7.5 human years. The research formula treats the same puppy as about 20, and the calculator does not apply it under 8 weeks, showing a note instead of a number.
| Puppy age | Size chart, any size | Research formula |
|---|---|---|
| 8 weeks | 2.3 | 1 |
| 3 months | 3.8 | 8.8 |
| 4 months | 5 | 13.4 |
| 6 months | 7.5 | 19.9 |
| 9 months | 11.3 | 26.4 |
| 12 months | 15 | 31 |
Puppies grow so fast that either number is a loose guide. If vaccines, food or spay and neuter timing depend on age, ask your vet rather than rely on the conversion.
Dog age by breed and weight
The size class follows adult weight, so use your dog's weight (or its expected adult weight, for a puppy) and check which class it falls in. The examples below are typical adult sizes, and individual dogs vary. A German shepherd or a pit bull type can sit on the edge of two classes, so go by the actual weight on the scale.
| Size class | Adult weight | Typical breeds |
|---|---|---|
| Small | Up to 20 lb (9 kg) | Chihuahua, Pomeranian, Yorkshire terrier, Jack Russell terrier, most Cavapoos |
| Medium | 21 to 50 lb (10 to 22 kg) | Border collie, Staffordshire bull terrier, cocker spaniel, French bulldog |
| Large | 51 to 100 lb (23 to 45 kg) | Labrador retriever, golden retriever, German shepherd |
| Giant | Over 100 lb (over 45 kg) | Great Dane, Saint Bernard, mastiff |
For a mixed breed or crossbreed, ignore the guessed parentage and use the weight alone. A puppy's adult weight is a vet's estimate, so enter the class they give you.
What are the dog life stages?
The American Animal Hospital Association (AAHA) divides a dog's life into five stages in its 2019 Canine Life Stage Guidelines: puppy, young adult, mature adult, senior and end of life. The stages follow growth and maturity rather than a single age, so the calculator labels your dog from its age and, where you give it, its expected lifespan.
| Stage | AAHA 2019 definition | Calculator label |
|---|---|---|
| Puppy | Birth until rapid growth stops, about 6 to 9 months depending on breed and size | "Puppy" under 6 months, "Puppy to young adult" from 6 to 9 months |
| Young adult | Until physical and social maturity, which most dogs reach by 3 to 4 years | "Young adult" from 9 months to 3 years, "Young to mature adult" from 3 to 4 years |
| Mature adult | Until the last 25% of estimated lifespan, which depends on breed and size | "Mature adult" from 4 years until the senior age |
| Senior | The last 25% of estimated lifespan, through end of life | "Senior" from 75% of the expected lifespan you enter, or a size-class age if you leave it blank |
| End of life | The terminal stage, which depends on the illness | Not age-based, so not shown |
When does a dog become senior? The last 25% rule
AAHA does not set one senior age. It calls a dog senior for the last 25% of its estimated lifespan, which depends on breed and size, and it suggests estimating lifespan from the breed. A dog expected to live 12 years is senior from 9, and one expected to live 16 years from 12. Enter your dog's expected lifespan to use that rule.
| Expected lifespan | Senior stage starts at |
|---|---|
| 10 years | 7.5 years |
| 12 years | 9 years |
| 14 years | 10.5 years |
| 16 years | 12 years |
If you leave the lifespan blank, the calculator falls back to a senior age by size: 7 years for small and medium dogs, 6 for large and 5 for giant. That fallback is our approximation, because AAHA publishes no per-size ages, and your vet's estimate for your dog's breed should replace it.
How do you work out a dog's age from its birthday?
Count the full months since the birthday and enter that number with Months selected. A dog born on January 20 is 21 months old on October 20 of the next year, which the size chart reads as 15 + (9 × 0.75) = 21.75 human years. Our Age Calculator gives exact years, months and days from any date.
Why do larger dogs age faster?
The chart's higher yearly add-on for large and giant dogs reflects the common observation that larger breeds have shorter lives. We could not tie the add-ons to a primary source, and the research formula has no size term because it was built from one breed, so treat the chart as a rule of thumb.
Signs your dog may be entering its senior years
These are common owner observations, not drawn from a cited source.
- Shorter or slower walks, and less interest in fetch.
- Stiffness getting up, or hesitation before stairs.
- More time asleep during the day.
- Gray hair around the muzzle.
None of these confirms a problem, and a sudden change at any age is a reason to call your vet. Food needs change with age and neutering, so recheck the daily amount with our Pet Food Calculator. If you also own a cat, the Cat Age Calculator shows its life stage on a separate curve. Planning a litter? The Dog Pregnancy Calculator estimates a whelping window from the mating date.
Is the dog age calculator different in the UK, Australia and Canada?
The math is the same in the US, UK, Australia and Canada. The size classes show kilograms next to pounds for readers in those countries. UK and Australian owners often say "crossbreed" or "pedigree", and both work here, because the class depends only on weight.
Frequently asked questions
Take a 7-year-old Labrador, which is a large dog. The size chart gives 24 + (5 × 5) = 49 human years, and the research formula gives 16 × ln(7) + 31, about 62. Enter the age and the size class and the calculator shows both.
No. A flat 7 would make a 1-year-old dog 7, while both models here put it far older, at 15 on the chart and 31 on the research formula. It would also give a 12-year-old dog 84 whatever its size, where the chart gives 64 for a small dog and 84 for a giant.
Use the chart to compare dogs of different sizes, because it is the only one with a size input. Treat the research formula as a check for Labrador-sized adults. When they disagree, your vet's view of your dog's condition counts for more than either.
On this chart, yes, and the gap widens every year after the second. At 5 years a small dog reads 36 and a giant dog 42. At 10 years it is 56 against 72, and at 15 years 76 against 102. Treat the difference as an assumption in the chart, not a measured rate, and compare your dog with others of its own size.
You can read it, but it ignores size. A 10-year-old Chihuahua and a 10-year-old Great Dane both come out at 68 on the formula, while the chart puts them 16 years apart, at 56 and 72. For a very small or giant dog, use the formula as a loose check on the chart, not as the main answer.
Use the size box: weight decides the class and the breed is only a hint. For a puppy, ask your vet for its expected adult weight.
Choose Weeks and type 10 for a 10-week-old puppy. The chart gives about 2.9 human years and the research formula about 4.6. The two are far apart this young, so use either as a loose guide.
At age 10 the chart's gap between a small and a giant dog is 16 human years (56 against 72), so it is worth asking your vet to estimate the adult weight of an unknown mix. If you do not know the birthday, a vet can estimate age from teeth and general condition, and you can enter the middle of that range.
There is no single age. AAHA ties the senior stage to the last 25% of a dog's estimated lifespan, so a dog expected to live 8 years is senior from 6 and one expected to live 15 years from 11.25. Until you enter a lifespan, the calculator uses 7, 6 or 5 years by size as our approximation.
It is an estimate, and the gap between the two methods shows how wide the margin is: for a 5-year-old small dog the chart says 36 and the formula says 57. Genetics, health and lifestyle change how fast a given dog ages, so a vet's exam of your dog says more than either number.
Sources and methodology
The research formula is from Wang et al., Cell Systems, 2020 (human age = 16 ln(dog age) + 31, built from 104 Labrador retrievers), with the 8-week and 12-year matches taken from the paper itself (the National Institute on Aging also published a release on the study). The size-adjusted chart is a simplified version of charts published by vets and pet sites. The life stages follow the AAHA 2019 Canine Life Stage Guidelines. We could not read a primary source for the chart's per-size increments or for the fallback senior ages by size, so those, and the weight bands (up to 20, 21 to 50, 51 to 100 and over 100 lb), are our approximation. The 6 and 9 month and 3 and 4 year cut points for the in-between labels are the ends of AAHA's ranges. Month and week values are our own straight-line estimates.