Puppy
Ask your vet about puppy nutrition, vaccination timing and safe exercise while they grow.
Free dog care tool
No email required
Dog age calculator
Convert dog years to human years.
How old is my dog in human years?
There is no exact conversion. Dogs develop quickly early in life, then aging varies with size and individual health. A common starting point is about 15 human years at age one and 24 at age two.
Using this calculator’s simplified size model, a five-year-old small dog is about 36 in human years. A five-year-old large dog is about 42. The difference helps explain why multiplying every dog’s age by seven misses the bigger picture.
Dog age chart by breed size
Compare estimated human years for small, medium, large and giant dogs. This table uses the same simplified model as the calculator, so the numbers stay consistent.
| Dog age | SmallUp to 20 lb (9 kg) | Medium21–50 lb (over 9–23 kg) | Large51–100 lb (over 23–45 kg) | GiantOver 100 lb (45 kg) |
|---|---|---|---|---|
| 6 months | 7.5 | 7.5 | 7.5 | 7.5 |
| 1 year | 15 | 15 | 15 | 15 |
| 2 years | 24 | 24 | 24 | 24 |
| 3 years | 28 | 29 | 30 | 31 |
| 4 years | 32 | 34 | 36 | 38 |
| 5 years | 36 | 39 | 42 | 45 |
| 6 years | 40 | 44 | 48 | 52 |
| 7 years | 44 | 49 | 54 | 59 |
| 8 years | 48 | 54 | 60 | 66 |
| 9 years | 52 | 59 | 66 | 73 |
| 10 years | 56 | 64 | 72 | 80 |
| 11 years | 60 | 69 | 78 | 87 |
| 12 years | 64 | 74 | 84 | 94 |
| 13 years | 68 | 79 | 90 | 101 |
| 14 years | 72 | 84 | 96 | 108 |
| 15 years | 76 | 89 | 102 | 115 |
| 16 years | 80 | 94 | 108 | 122 |
Puppy values are interpolated estimates. Size categories use adult weight. The table is a guide, not an official veterinary chart.
How to calculate dog years to human years
The size-adjusted estimate used here
Our simplified model counts the first year as 15 human years and the second as another nine. After age two, it adds four human years per dog year for small dogs, five for medium dogs, six for large dogs and seven for giant dogs. These size adjustments are a practical approximation, not a validated formula for each breed.
After age two: human years ≈ 24 + (dog age − 2) × size factor
Example: a five-year-old small dog is 24 + (5 − 2) × 4 = 36 human years. For part-years, the calculator estimates between these values.
Why one dog year is not seven human years
The seven-year rule assumes a steady pace throughout life. It misses rapid puppy development and treats dogs of every size the same. Use human years as a comparison, then plan care around your individual dog.
The DNA methylation research formula
A study published in 2020 compared DNA methylation patterns in 104 Labrador Retrievers with those in humans. It proposed a different relationship: H = 16 × ln(D) + 31, where D is dog age in years and ln is the natural logarithm.
This research describes one aspect of biological aging in the dogs studied. It is not a universal breed calculator, which is why it is explained separately from your result.
How breed and size affect dog aging
Larger dogs generally have shorter lifespans than smaller dogs, but breed, genetics and health also matter. Selecting a breed here suggests an adult-size category. It does not apply a separate scientific formula for that breed.
At eight years old, a Chihuahua may still be a mature adult while a Great Dane may already be a senior. Our illustrative stage thresholds reflect that difference. They do not predict how long either dog will live.
For a mixed breed or a breed not listed, choose their expected adult size. Enter their age in years and months. If you’re unsure of their age, use your best estimate.
Dog life stages and what they mean for care
AAHA describes four stages: puppy, young adult, mature adult and senior. Their timing varies. This tool uses approximate size-based thresholds; your vet can help identify the stage and care needs of your dog.
Young adult
Match exercise to your dog, build a dental routine and keep parasite prevention and vaccinations up to date.
Mature adult
Track weight and changes in activity. Discuss nutrition, dental care and preventive checks with your vet.
Senior
Discuss check-up frequency and any changes in comfort, sleep or appetite with your vet. Adapt exercise to their abilities.
At every age, track weight, maintain dental care and discuss nutrition, exercise, vaccinations and parasite prevention with your vet. Record new changes rather than assuming they are just part of getting older.
AAHA defines senior as the final quarter of an estimated lifespan. Our displayed ages are illustrative guides, not an individualized AAHA assessment.
Dog age calculator FAQs
Is one dog year equal to seven human years?
No. Dogs develop much faster in their first two years, and their later aging varies with size. A fixed seven-to-one conversion leaves out both differences.
How old is a five-year-old dog in human years?
In this simplified calculator, about 36 for a small dog, 39 for a medium dog, 42 for a large dog and 45 for a giant dog. Different age charts can give different estimates.
Does this calculator use my dog’s breed?
It uses common breeds to suggest an adult-size category. You can adjust that size to match your dog. Dogs of the same size get the same human-year estimate; there is no unique formula for each breed.
What if I don’t know my dog’s birthday?
Enter their age directly in years and months. You don’t need their date of birth. If you’re unsure, your vet may help estimate age from dental development, medical history and a physical examination.
When is a dog considered a senior?
It varies with expected lifespan, breed and individual health. Giant dogs often reach their senior stage earlier than small dogs. The life stage shown here is a general guide to discuss with your vet.
How accurate are dog years to human years calculators?
They provide a useful comparison, not a biological measurement. Two dogs of the same age can have different health and care needs. This tool does not diagnose conditions or predict lifespan.
Is the dog age calculator free?
Yes. Use the calculator and share your result without an account. To keep your dog’s care reminders, weight and health records together, download DogCat.
Sources and calculation notes
The sources below explain dog development, life stages and the research behind human-age comparisons. The size factors and displayed stage thresholds are DogCat’s simplified estimates.
Luna
Pup
Deworming
Weekly weigh-in
28.80 kgOct 11, 2026 · 08:00