Dog Age Calculator
A dog's age in human-equivalent years on the veterinary size-based chart, with the 2019 epigenetic formula alongside for adult dogs.
Dogs mature fast and then age at a rate that depends on size: the first year is about 15 human years, the second reaches 24, then each dog year adds four (small), five (medium) or six (large) human years.
How the dog age calculator works
Dogs mature fast and then age at a rate that depends on size: the first year is about 15 human years, the second reaches 24, then each dog year adds four (small), five (medium) or six (large) human years. The epigenetic method (16 × ln(age) + 31) comes from DNA-methylation clocks and applies to adult dogs; under one year the chart is used.
Formula: Human years = 24 + (age − 2) × rate (4 small · 5 medium · 6 large) · Epigenetic: 16 × ln(age) + 31
How dog years convert to human years
Fast at first, then steady
Dogs don't age at a constant rate, so multiplying by a single number never works. They grow up quickly: by the end of their first year a dog is roughly a 15-year-old human, and by the end of the second year around 24. After that the pace settles into a steadier climb — each extra dog year adds about +4 human years for a small dog, +5 for a medium dog and +6 for a large dog. That size split is the important part: bigger dogs age faster and reach old age sooner, so the same calendar age lands at a higher human number for a Great Dane than for a Jack Russell.
Worked example
A 5-year-old medium dog: 15 (year one) + 9 (year two) then 3 more years at +5 = 24 + 15 ≈ 39 human years. A 10-year-old large dog: 24 by year two, then 8 more years at +6 = 24 + 48 ≈ 72 human years. Switch the method to the epigenetic formula and the same dog gets a science-based second opinion — the two won't always agree, and that's fine.
This is a friendly estimate, not a health check. Real ageing depends on breed, genetics, weight and care. Use the human-years figure as a nudge — for a senior dog that means twice-yearly visits to your vet, joint and dental care, and keeping them lean. Your vet's assessment always overrides this tool.
Why size mattersWhy bigger dogs age faster
Among dogs, size and lifespan run in opposite directions — the largest breeds live the shortest lives, so each of their years counts for more. That's why this calculator uses a different "per year" step for each size group after the first couple of years:
- Small (under 10 kg) — +4 human years/year. Toy and small breeds such as a Chihuahua or Jack Russell often reach 15–16 years, so they age the most gently.
- Medium (10–25 kg) — +5 human years/year. Border Collies, Cocker Spaniels and Staffies sit in the middle of the range.
- Large (over 25 kg) — +6 human years/year. Labradors, German Shepherds and giant breeds like a Great Dane reach senior age earliest, sometimes by 6–7.
The first two years are the same for every size — about 15 then 24 — because all dogs pack their fast growing-up phase into that window. It's only afterwards that the paths diverge. If your dog sits on the boundary between two groups, try both and read the pair as a range rather than a single exact age.
The epigenetic formulaThe 2019 epigenetic formula, explained
A logarithm, not a multiplier
In 2019 researchers at UC San Diego compared chemical "clock" marks on DNA — methylation — in Labrador Retrievers and in people, and found the two lined up along a curve. The result is a formula: human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. Because it's logarithmic, it climbs steeply for young dogs and then flattens: a 1-year-old comes out around 31, a 4-year-old around 53, and a 10-year-old around 68.
How to read it
The epigenetic curve is a genuine research finding, but it was built mainly on one breed, so it doesn't split by size the way the vet chart does. Treat it as a scientific second opinion rather than a breed-specific answer. For very young puppies it can read high — under a year the formula isn't really meant to apply — so for a puppy the size-based chart is the friendlier guide. Flip between the two methods and you'll see where they agree and where they don't.
Frequently asked Frequently asked questions
Where these figures come from
The methods here are the mainstream ways vets and researchers translate a dog's age. Dog ageing is biology, not a country-specific rule, so the same numbers apply wherever you live.
- Size-based chart — year one ≈ 15 human years, year two ≈ 24, then about +4 (small, under 10 kg), +5 (medium, 10–25 kg) or +6 (large, over 25 kg) per dog year. This is the widely used veterinary rule of thumb.
- Epigenetic formula — human age = 16 × ln(dog age) + 31, from the 2019 UC San Diego study of DNA methylation in Labrador Retrievers (Wang et al.).
- Life stages — puppy, adolescent, adult, mature and senior, following the canine life-stage framework used in veterinary practice.
- Breed lifespans — small breeds commonly 14–16 years, large and giant breeds often 7–10, which is why size changes the per-year step.
- Further guidance — RSPCA — pet care guidance.
Last checked: July 2026. This is a fun, informative estimate, not veterinary advice. Individual dogs vary with breed, genetics, weight and health — your vet's assessment of your own dog always comes first.
Understanding your resultSelect the question that matches where you are right now.
The headline number is your dog's age translated into human years — how grown-up they'd be if they were a person. The breakdown shows the life stage behind it and how the size-based chart and the epigenetic formula compare.
What to do with itUse it as a sense-check on life stage. A number in the 40s says mature adult; the 60s and beyond say senior — a cue for twice-yearly vet checks, joint care and keeping your dog lean.
What it is notIt's not a health assessment or a lifespan prediction. Two dogs the same "human age" can be in very different shape depending on breed, genetics, weight and care.
Why not just ×7The old ×7 rule gets a young dog badly wrong — a 1-year-old is closer to 15 than 7 — and misreads the senior years too. Size-based ageing matches real life far better.
Two things move the human-years figure the most: your dog's age and their size or breed group. The method you choose is the third.
Age & the early yearsThe first two years count for the most — about 15 then 24 human years — because dogs do their growing-up fast. After that the climb is steadier.
Size / breed groupSmall dogs add ~4 human years a year, medium ~5 and large ~6. Bigger dogs reach senior age earlier, so size can shift the answer by years.
Method: chart vs epigeneticThe vet chart splits by size; the 2019 epigenetic formula (16 × ln age + 31) is a single research curve built mainly on Labradors. Compare the two and read them as a range.
The number is only useful if it prompts good care. A few habits keep an ageing dog healthy.
Keep them leanExtra weight shortens a dog's life and worsens joints. Feed to body condition — you should feel the ribs with a light cover and see a waist from above.
Vet checks by life stageAdults do well with a yearly check; seniors benefit from twice-yearly visits so problems are caught early. Dental and joint care matter more with age.
Match food to the stagePuppies, adults and seniors have different needs. Portion to the dog in front of you rather than the number on the bag.
A dog is a long-term commitment — and a line in the household budget. Plan the costs alongside the cuddles.
The whole household billSee where a pet fits alongside your other running costs.
Cost of living → Budget for food and insuranceGive the monthly pet spend a proper line of its own.
Budget planner → A buffer for the vet billBuild a rainy-day fund for the unexpected vet visit.
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The 'multiply by 7' myth Year 1 ≈ 15 human years
The old rule that one dog year equals seven human years is wrong. Dogs mature much faster early on — a one-year-old dog is roughly a 15-year-old human, and by age two it's about 24. After that, ageing slows to about 4–6 human years per dog year depending on size. So a straight ×7 badly underestimates a young dog and overestimates a middle-aged one. Use a proper chart instead.
| Year 1 | ≈15 human |
|---|---|
| Year 2 | ≈24 human |
| ×7 rule | A myth |
- Young dogs Age fast
- Then ~4–6/yr
Why size changes dog age Small live longer
Body size strongly affects how fast a dog ages. Small breeds (under 10 kg) add about 4 human years per dog year after age two, medium breeds about 5, and large or giant breeds about 6 — so a big dog is a senior years earlier. At 10 years old a small dog is about 56 in human terms, a medium about 64, and a large about 72. It's why giant breeds sadly have shorter lifespans than toy breeds.
| Small +/yr | ~4 years |
|---|---|
| Medium +/yr | ~5 years |
| Large +/yr | ~6 years |
- 10-yr small ≈56 human
- 10-yr large ≈72 human
How old is a 5-year-old dog? 36–42 human years
A 5-year-old dog is about 39 in human years for a medium breed (24 for the first two years, then three years at +5). A small breed of the same age is around 36, and a large breed about 42. That puts a 5-year-old dog squarely in confident adulthood — old enough for a baseline senior health check if it's a large breed, still comfortably middle-aged for a small one.
| Small | ≈36 years |
|---|---|
| Medium | ≈39 years |
| Large | ≈42 years |
- Life stage Adult
- Large breeds Baseline check
Is a 10-year-old dog old? 56–72 human years
Yes — a 10-year-old dog is a senior. In human terms that's about 56 for a small breed, 64 for a medium, and 72 for a large one. This is the age to step up preventive care: twice-yearly vet checks, blood work to catch kidney or thyroid issues early, joint support, and a diet suited to a slower metabolism. Many dogs stay happy and active well into their teens with good care.
| Small | ≈56 years |
|---|---|
| Medium | ≈64 years |
| Large | ≈72 years |
- Vet checks Twice a year
- Watch for Joint + organ issues
The 2019 epigenetic formula 16 × ln(age) + 31
A 2019 University of California study measured DNA methylation — chemical 'ageing marks' on DNA — in dogs and people, and produced the formula human_age = 16 × ln(dog_age) + 31. It maps a 1-year-old dog to about 31 and an 8-year-old to about 64. It captures the fast-then-slow ageing curve elegantly but is based on Labradors and doesn't adjust for size, so for everyday use the size-based chart is usually more practical.
| Formula | 16 × ln(age) + 31 |
|---|---|
| Dog age 1 | ≈31 human |
| Dog age 10 | ≈68 human |
- Based on Labradors
- No Size adjustment
Puppy, adult, senior — the life stages Senior from ~7
Dogs move through puppy (birth to ~9 months), adolescent (to ~2 years), adult (2–7), mature (7–10) and senior (10+), though large breeds reach each stage earlier. Vets increasingly recommend a senior wellness check from around age seven — earlier for big dogs — even in a healthy dog, because catching arthritis, dental disease and organ changes early makes them far easier to manage.
| Puppy | To ~9 months |
|---|---|
| Adult | 2–7 years |
| Senior | From ~7–10 |
- Large breeds Age earlier
- Senior check From ~7
Worked examples
| Inputs | Human-equivalent age | Note |
|---|---|---|
| A 3-year-old medium dog | 29 human years | 29 human years |
| A 10-year-old large dog | 72 human years | 72 — senior |
| A 5-year-old dog by the epigenetic formula | 57 human years | about 57 |
FAQFrequently asked questions
How old is my dog in human years?
It's not a simple multiplication. Dogs mature fast early and then slow down, and bigger dogs age quicker than small ones. A good rule of thumb from vet charts: the first year of a dog's life is worth about 15 human years, the second adds about 9 more (so a 2-year-old dog is roughly 24), and after that each dog year adds about 4 human years for a small dog, 5 for a medium dog and 6 for a large dog. So a 5-year-old medium dog is about 39 in human terms, and a 10-year-old large dog is about 72.
Is one dog year really seven human years?
No — the ×7 rule is a myth. It seems to have come from simply dividing a rough human lifespan of about 70 by a dog lifespan of about 10, but it doesn't match how dogs actually age. Dogs reach adulthood in their first year or two — a 1-year-old dog is closer to a 15-year-old human than a 7-year-old — and then age more slowly. The ×7 rule badly underestimates a young dog's maturity and gets the later years wrong too, which is why vets use a size-based chart instead.
Why do bigger dogs age faster?
Larger breeds live shorter lives and reach old age sooner, so each calendar year counts for more. A small dog such as a Jack Russell may live 15–16 years, while a giant breed like a Great Dane often lives only 7–8. To reflect that, this calculator adds about 4 human years per dog year for small dogs, 5 for medium and 6 for large after the first couple of years. It means two dogs the same age can have quite different human-equivalent ages if one is a lap dog and the other a giant breed.
How old is a 10-year-old dog?
It depends on size. Using the vet size-based chart — 15 for year one, 24 by year two, then 4/5/6 human years per year after that — a 10-year-old small dog is about 56 in human terms, a medium dog about 64, and a large dog about 72. All three are firmly in the senior stage, which is a good prompt for twice-yearly vet checks, joint and dental care, and an eye on weight.
What is the epigenetic dog age formula?
In 2019 researchers at UC San Diego measured chemical changes to DNA (methylation) in Labrador Retrievers and humans and found a matching curve. Their formula is human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. It captures how fast dogs age when young — a 1-year-old dog comes out around 31 — and then flattens out. It was built mainly on one breed, so treat it as a scientific alternative to the size-based chart rather than a breed-specific answer; this calculator lets you switch between the two. Sources
The sources behind this calculator
- American Association of Feline Practitioners — Feline Life Stage Guidelines — the six feline life stages the cat-age page uses
- Wang et al. 2020, Cell Systems — Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome — the 16·ln(age)+31 epigenetic formula on the dog-age page
- UK Government — Tips at work — the law on how tips are shared with staff
Last checked: September 2026. Where a page states a convention (a tipping custom, a pet life stage), the page names the body it follows.