Dog and cat age calculator (human-age estimate)
Enter a birth date or an estimated age to see a dog or cat’s approximate human-age equivalent and life-stage labels.
dog · cat · human-age estimate
Estimate your pet’s human age
Human-age estimate · life-stage reference
Choose the pet, dog size and age. The result updates automatically.
Enter your pet’s age.How to use the dog and cat age calculator
This calculator converts dog and cat ages to an approximate human-age equivalent. Its reference model maps the first year to 15 human years, age 2 to 24, then adds +4~7 per year according to dog size. It also displays simplified life-stage labels with AAHA/AAFP guideline context. Multiplying every pet year by 7 misses the model’s faster early development. None of these human-age numbers measures an individual animal’s biological age or replaces a veterinary assessment.
Human-age conversion is an illustration, while actual preventive care depends on the animal. Nutrition and vaccinations in young pets, and checkups and mobility in older pets, are topics to discuss with your veterinarian. If an adopted dog or cat has no known birth date, choose estimated age and use the same conversion model. Calculations run in your current browser and the tool does not save the entered birth date or age.
When this tool is needed
- See a rough human-age equivalent for your dog or cat.
- Compare how the model changes between small, medium and large dogs.
- Use a veterinary age estimate when an adopted pet’s birth date is unknown.
Check before entering
- For dogs, choose the expected adult-weight category: small ~9kg, medium 10~23kg or large 24kg~.
- Cats use the same model regardless of weight, adding +4 human years per year from age 3.
- Estimated age accepts whole months 0~11 and a whole-year value up to 25.
How to use
- Choose dog or cat.
- For a dog, choose its expected adult size: small, medium or large.
- Choose birth date or estimated age.
- Enter the birth date, or estimated years and months. The result updates immediately.
- Read the human-age estimate and life stages. Use Copy result if you want the summary on your clipboard.
Dog-to-human age table (1~16 years, by size)
The table uses this calculator’s formula. Ages 1 and 2 map to 15 and 24 human years for every dog size. From age 3, add +4 for small dogs, +5 for medium dogs or +7 for large dogs each year. Months are interpolated proportionally: a small dog aged 3 years 6 months displays about 30 human years.
| Dog age | Small~9kg | Medium10~23kg | Large24kg~ |
|---|---|---|---|
| 1 yr | 15 yrs | 15 yrs | 15 yrs |
| 2 yrs | 24 yrs | 24 yrs | 24 yrs |
| 3 yrs | 28 yrs | 29 yrs | 31 yrs |
| 4 yrs | 32 yrs | 34 yrs | 38 yrs |
| 5 yrs | 36 yrs | 39 yrs | 45 yrs |
| 6 yrs | 40 yrs | 44 yrs | 52 yrs |
| 7 yrs | 44 yrs | 49 yrs | 59 yrs |
| 8 yrs | 48 yrs | 54 yrs | 66 yrs |
| 9 yrs | 52 yrs | 59 yrs | 73 yrs |
| 10 yrs | 56 yrs | 64 yrs | 80 yrs |
| 11 yrs | 60 yrs | 69 yrs | 87 yrs |
| 12 yrs | 64 yrs | 74 yrs | 94 yrs |
| 13 yrs | 68 yrs | 79 yrs | 101 yrs |
| 14 yrs | 72 yrs | 84 yrs | 108 yrs |
| 15 yrs | 76 yrs | 89 yrs | 115 yrs |
| 16 yrs | 80 yrs | 94 yrs | 122 yrs |
Values for large dogs aged 16 or more can look exaggerated because of the model’s limits. Treat the table as a rough illustration within typical lifespans, not a longevity forecast.
Cat-to-human age table (1~20 years)
Cats use 15 human years at age 1, 24 at age 2 and +4 per year after that, regardless of weight. Whole-year values match the AAFP/AAHA 2010 table. This tool’s fractional-month interpolation differs: it displays 7 human years at 6 months and 19 at 18 months, whereas the reference gives 10 and 21.
| Cat age | Human age | Cat age | Human age |
|---|---|---|---|
| 1 yr | 15 yrs | 11 yrs | 60 yrs |
| 2 yrs | 24 yrs | 12 yrs | 64 yrs |
| 3 yrs | 28 yrs | 13 yrs | 68 yrs |
| 4 yrs | 32 yrs | 14 yrs | 72 yrs |
| 5 yrs | 36 yrs | 15 yrs | 76 yrs |
| 6 yrs | 40 yrs | 16 yrs | 80 yrs |
| 7 yrs | 44 yrs | 17 yrs | 84 yrs |
| 8 yrs | 48 yrs | 18 yrs | 88 yrs |
| 9 yrs | 52 yrs | 19 yrs | 92 yrs |
| 10 yrs | 56 yrs | 20 yrs | 96 yrs |
Month-based estimates for dogs and cats under 12 months
The first 1 year distributes 15 human years across 12 months; the second distributes 9. The displayed result is rounded down. Dogs and cats use the same early-age calculation.
- Age 1 month ≈ 1 human year · 3 months ≈ 3
- Age 6 months ≈ 7 human years · 9 months ≈ 11
- Age 11 months ≈ 13 human years
- Age 1 year 3 months ≈ 17 · 1 year 6 months ≈ 19 human years
- Age 1 year 9 months ≈ 21 · 2 years = 24 human years
Dog-age formula at a glance
Human age = 24 + (pet years − 2) × factor (from age 3: small 4, medium 5, large 7, cat 4). Age 1 maps to 15 and age 2 to 24.
- Medium dog aged 6 → 24 + (6 − 2) × 5 = 44 human years
- Large dog aged 9 → 24 + (9 − 2) × 7 = 73 human years (model senior)
- Cat aged 12 → 24 + (12 − 2) × 4 = 64 human years
Choosing a dog-size category
Larger dogs generally have shorter lifespans, so this model assigns a higher human-age factor and an earlier senior threshold. Choose the category from expected adult weight. The model does not take breed, medical history or an individual lifespan estimate as inputs.
- Small (~9kg): +4 per year from age 3; model senior threshold about 11. The page’s broad lifespan illustration is 12~16 years, not an individual prediction.
- Medium (10~23kg): +5 per year; model senior threshold about 10. Broad lifespan illustration: 10~13 years.
- Large (24kg~): +7 per year; model senior threshold about 7. Broad lifespan illustration: 8~11 years.
- Cat: +4 per year regardless of weight; this model starts senior at about 11. The AAHA/AAFP 2021 guideline says over 10 years. The page’s indoor-cat lifespan illustration is 12~18 years, not a forecast.
Human-age estimates and veterinary life stages differ
Human age here is a reference or fun estimate. Veterinary care uses the animal’s life stage and individual condition. The veterinary-stage line in the result approximates the definitions below with fixed age cutoffs. Those cutoffs describe this calculator and are not an individual clinical classification.
- The human-age result is a reference value. AVMA also publishes an example table, but its dog values are not all identical to this calculator’s size-based factors. Neither is an individual health diagnosis.
- AAHA 2019 canine guidance: puppy (rapid growth ending around 6~9 months), young adult (maturation around 3~4 years), mature adult and senior (last 25% of estimated lifespan): 4 age-related stages.
- AAHA/AAFP 2021 feline guidance: kitten (~1 year), young adult (1~6 years), mature adult (7~10) and senior (over 10): 4 age-related stages.
- This calculator fixes senior thresholds at small dog 11, medium 10, large 7 and cat 11. These are approximate model assumptions; actual classification varies by breed and individual animal.
- Research comparison: the UCSD 2020 epigenetic-clock study (Wang et al., Cell Systems) proposed human age ≈ 16 × ln(dog age) + 31 (age 1 ≈ 31 and age 5 ≈ 57). This calculator does not use that formula.
Understanding dates and displayed ages
Birth-date calculations use the browser’s local calendar date. The day counter adds 1 to elapsed days, counting the birth date as day 1. At the same instant, different time zones may therefore show different local dates. Human age distributes months proportionally, then rounds down; it is not a precise biological age. Estimated age uses months 0~11 and a whole-year value up to 25.
Sources and limits
The tool’s reference model uses 15 human years in the first year, 9 in the second and then 4~7 by size. Cat whole-year comparison: AAFP/AAHA Feline Life Stage Guidelines 2010; stage context: AAHA Canine Life Stage Guidelines 2019 and AAHA/AAFP Feline Life Stage Guidelines 2021; epigenetic study: Wang et al., Cell Systems 2020. The factors 4,5,7 and monthly interpolation are simple assumptions and do not match every value in those sources. Original calculations were retained; explanations, sources and date boundaries were checked on 2026-10-31. See the AVMA example table, AAFP/AAHA 2010 table, AAHA canine stages. Wang’s study used 104 Labrador retrievers. This tool does not calculate its epigenetic formula.
Human-age conversion is an approximate reference, not a veterinary diagnostic standard. Aging and health vary with breed, constitution and environment. Discuss diagnosis, treatment and an individual care plan with your veterinarian.
FAQ
How old is a 1-year-old dog in human years?
This model gives about 15 human years at age 1 and about 24 at age 2, then adds 4~7 each year by size. A flat age × 7 comparison misses its early-development assumption. The first year adds 15 and the second 9; later factors depend on dog size. This is an illustration, not an individual biological-age or health measurement.
What formula does the dog-age calculator use?
Age 1 maps to 15 human years and age 2 to 24. From age 3, add +4 per year for small dogs, +5 for medium and +7 for large. A small dog aged 5 gives 24 + 3 × 4 = 36; a large dog aged 5 gives 24 + 3 × 7 = 45. Months are proportional and the display rounds down: 6 months gives about 7, and 1 year 6 months about 19 human years.
Why do small and large dogs give different results?
The model assigns a larger annual factor to larger dogs, reflecting broad size-related lifespan differences. At age 10 it gives about 56 human years for small, 64 for medium and 80 for large dogs. Its senior thresholds are about 11,10,7 respectively; those are fixed model assumptions, not individual clinical cutoffs. Choose expected adult weight: small ~9kg, medium 10~23kg or large 24kg~.
How is a cat’s human age calculated?
Cats use 1 year = 15 human years, 2 = 24, then +4 each year regardless of weight: age 5 gives 36, 10 gives 56 and 15 gives 76. Whole-year values match the AAFP/AAHA 2010 table; monthly interpolation does not. The 2021 guidance calls ages 7~10 mature adult and over 10 senior. This code uses completed whole years and starts its senior label at age 11.
Is a human-age estimate a veterinary measurement?
No. It is an approximate illustration, not an official veterinary diagnostic standard. The AAHA 2019 dog guidance distinguishes 4 age-related stages: puppy, young adult, mature adult and senior, with senior referring to the last 25% of estimated lifespan. Individual breed and lifespan matter rather than one fixed year. A UCSD 2020 epigenetic study proposed human age ≈ 16 × ln(dog age) + 31 (age 1 ≈ 31, age 5 ≈ 57); this calculator uses a different model. Discuss medical decisions with your veterinarian.