Dog and Cat Age Calculator: Pet Years in Human Years
Choose dog or cat, enter the age and, for a dog, the adult size. You get the human-age equivalent, the life stage and what changes at the next birthday. Dogs get two published methods side by side; the formulas and sources are below
About Your Pet
Valid range for dogs: 3 months to 25 years
Not sure of the birthday? Use your best estimate. For a rescue animal, a veterinarian can estimate the age.
Weight the dog reaches or has reached as an adult
Only changes when “Senior” starts
Valid range: 6–20 years
A human-age equivalent is a rough comparison, not a measurement. Ask your veterinarian about the care your own animal needs at this age.
An estimate for curiosity and planning, not veterinary advice.
Estimate, Not Veterinary Advice
This calculator gives a rough comparison for curiosity and planning. A human-age figure does not measure health and cannot tell you how your pet feels or what care it needs. Questions about food, check-ups or changes in behavior belong with your veterinarian. Your inputs stay in your browser.
How to use it
- Tap Dog or Cat at the top of the form.
- Enter the age in years and months. The tool accepts 3 months to 25 years for dogs and 3 months to 30 years for cats.
- For a dog, pick the adult size. The default lifespan of 12 years only affects when “Senior” starts, so change it if your veterinarian gives you a different figure for your breed.
- Read the human-age equivalent, the life stage, the second dog method and what changes at the next birthday.
- Press Copy Result to paste the numbers into a message.
Worked example
A medium-sized dog aged 5 years with the default lifespan of 12 years. Rule of thumb: 24 + 4.5 × (5 − 2) = 37.5, shown as 38 human years, with a range of 36–39 from the rates 4 and 5. Research formula: 16 × ln(5) + 31 = 56.8, shown as 57. Senior starts at 0.75 × 12 = 9 years, so the dog is a mature adult with 4 years to go. At the next birthday the rule adds 4.5 human years, to 42. A cat aged 10 years and 11 months: 24 + 4 × (10.92 − 2) = 59.7, shown as 60. It is still a mature adult, and senior starts in 1 month.
Why this tool exists and where its numbers come from
Owners want to translate a pet's age into a rough human equivalent and life stage. The dog formula (16 × ln(age) + 31) comes from a 2020 DNA-methylation study of 104 dogs, mostly Labradors, so it may not fit every breed; the size-based rule and the cat figures are rules of thumb.
Sources
For the full method, see the Methodology section just below.
Methodology
1. Rule of thumb by size. The first dog year counts as 15 human years and the second as 9 more, 24 in total. After that every dog year adds a fixed number: human age = 24 + rate × (dog age − 2). The rate follows the ranges that PetMD publishes for adult size: 4 for small dogs, 4–5 for medium, 5–6 for large and 7–8 for giant dogs. The headline uses the midpoint and the low–high range is shown beside it. Cats use the same start of 15 and 24 with a rate of 4. 2. Research formula for dogs. Wang et al. (Cell Systems, 2020) compared DNA methylation in 104 dogs, mostly Labrador retrievers, with humans and fitted human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. The curve rises fast in the first years and slowly later: about 31 for a 1-year-old dog and 71 for a 12-year-old. 3. Life stage is a separate calculation. Cats follow the 2021 AAHA/AAFP guidelines: kitten up to 1 year, young adult 1 to 6, mature adult 7 to 10, senior from 11 years. For dogs this tool uses puppy up to 9 months, young adult up to 4 years and senior from 75% of the lifespan you enter, because AAHA defines senior as the last 25% of the expected lifespan. Ages under 3 months, or above 25 years for dogs and 30 for cats, show “—” instead of a number.
Sources and documentation
The formula comes from the first entry, the life stages from the next two, and the size ranges from the PetMD pages. The 15 and 24 starting values are a widely repeated rule of thumb for which no primary study was found. Pages were consulted in October 2026; guidelines get updated, so check the originals.
- Wang et al. 2020, Cell Systems: dog-to-human aging by DNA methylationSource of human age = 16 × ln(dog age) + 31. Mostly Labrador retrievers; the paper is hosted on the authors’ lab site.
- AAHA/AAFP 2021 Feline Life Stage GuidelinesKitten, young adult, mature adult and senior age ranges for cats.
- AAHA 2019 Canine Life Stage Guidelines (PDF)Life stages for dogs; senior is the last 25% of the expected lifespan.
- PetMD: How old is my dog in human years?Rates per dog year by adult size. Veterinarian-reviewed article that cites no primary source.
- PetMD: How old is my cat in human years?The 15, 24 and +4 per year rule of thumb for cats. Secondary source.
Pet age by age: what the tool returns
Human years as the tool returns them, rounded to whole numbers. Where the size rule gives a range, it is shown as low–high. In the first two years every size gets the same 15 and 24; the sizes separate only afterwards. The research formula starts higher and, for medium dogs, crosses the rule at around 12 years.
| Pet age | Dog: research formula | Small dog | Medium dog | Large dog | Giant dog | Cat |
|---|---|---|---|---|---|---|
| 1 year | 31 | 15 | 15 | 15 | 15 | 15 |
| 2 years | 42 | 24 | 24 | 24 | 24 | 24 |
| 3 years | 49 | 28 | 28–29 | 29–30 | 31–32 | 28 |
| 5 years | 57 | 36 | 36–39 | 39–42 | 45–48 | 36 |
| 8 years | 64 | 48 | 48–54 | 54–60 | 66–72 | 48 |
| 10 years | 68 | 56 | 56–64 | 64–72 | 80–88 | 56 |
| 12 years | 71 | 64 | 64–74 | 74–84 | 94–104 | 64 |
| 15 years | 74 | 76 | 76–89 | 89–102 | 115–128 | 76 |
Read across a row to see the spread. A 10-year-old dog is 56 human years for a small dog, 80–88 for a giant one and 68 by the formula. That gap is real uncertainty, not rounding. Every value is an estimate for curiosity, not veterinary advice.
For Pets Getting On in Years
Two everyday items for an older dog or cat
EHEYCIGA Orthopedic Extra Large Dog Bed, 44 in, Waterproof and Washable, Egg-Crate Foam, Gray
An extra-large bed of about 44 inches (112 cm) with egg-crate foam and a waterproof, washable cover, according to the listing.
Veken C1 Classic Cat Water Fountain, 2.8 L (95 oz), with Replacement Filters and Silicone Mat, Gray
A 2.8-liter fountain that offers running water instead of a still bowl, with replacement filters and a silicone mat, according to the listing.
VOLUAS Automatic Cat Feeder, 4L Timed Dry Food Dispenser for Cats & Dogs
A timed dry-food dispenser with programmable portions and up to 4 meals a day, per the listing. It repeats the amount you set, so enter the grams from this page and check what it really delivers.
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Frequently asked questions
Is one dog year really 7 human years? ▼
No, the 7× rule is a round-number shortcut. It gives 7 for a 1-year-old dog, far below both methods here (15 by the rule of thumb and 31 by the research formula). For a 10-year-old it gives 70, which is above the 56–64 this tool’s rule gives small and medium dogs and close to the formula’s 68. Aging is fast early in life and slows later, which a single multiplier cannot capture.
Why does the tool show two results for a dog? ▼
Because published methods disagree and neither is a measurement of your dog. The size rule of thumb is simple and accounts for size; the 2020 research formula is based on DNA methylation but on mostly one breed. A 5-year-old medium dog is 38 by the first and 57 by the second. Showing both makes the uncertainty visible instead of hiding it behind one confident number.
How old is a cat in human years? ▼
By the common rule of thumb a cat is 15 at one year, 24 at two and then gains 4 human years per cat year: 36 at 5 years, 56 at 10 and 76 at 15. The AAHA/AAFP guidelines do not publish human equivalents; they define life stages (kitten, young adult, mature adult, senior), which the tool shows next to the number.
Does size or breed change the answer? ▼
For dogs, yes. Larger dogs tend to live shorter lives, so the rule counts them as older at the same age; that is why the tool asks for adult size. For a mixed breed, choose the size group closest to the weight the dog has or will reach. Cat breeds are not distinguished, and no breed-specific formula is used for dogs.
What life stage is my pet in? ▼
Cats: kitten up to 1 year, young adult 1 to 6, mature adult 7 to 10, senior from 11 (AAHA/AAFP 2021). Dogs: puppy up to 9 months, young adult up to 4 years, then mature adult until the last 25% of the expected lifespan, which is senior (AAHA 2019). Change the lifespan field if your veterinarian expects a different figure. Ask the veterinarian when check-ups or food should change.