Medically reviewed by our reviewing veterinarian, DVM · September 2026 Formulas, life stages and health notes follow AVMA, AKC and AAHA guidance. How we review · Not a substitute for veterinary advice.
How do you convert human years to dog years?
Divide by 15 for human ages under 15, then use the anchors 15 human years = 1 dog year and 24 = 2 dog years. Above 24, subtract 24, divide by your dog's yearly rate (4 toy and small, 5 medium, 6 large, 7 giant) and add 2. Human 41 for a medium dog is 2 + 17/5 = 5.4.
The conversion works backwards from the size-adjusted model published by the American Veterinary Medical Association: a dog's first year equals 15 human years, the second brings it to 24, and each later year adds 4 human years for toy and small dogs, 5 for medium, 6 for large and 7 for giant breeds. Reversing it takes three steps.
- Under 15 human years: divide by 15. Ten human years is 0.67 dog years, about 8 months.
- 15 to 24 human years: the dog is between 1 and 2 years old. Twenty human years is about 1.6 dog years.
- Over 24 human years: subtract 24, divide by the size rate, add 2. Sixty-five human years for a medium dog is 2 + 41/5 = 10.2 dog years.
The American Kennel Club describes the same staged approach, which is why the forward and reverse answers on this site always agree with each other.
How old is 3 human years in dog years?
Three human years is about 0.2 dog years, roughly 2.4 months, which is a recently weaned puppy about to leave its litter. Because dogs reach 15 human years by their first birthday, every human year before 15 corresponds to only about 24 days of puppy life, so small human ages become weeks and months.
Human ages under 15 all land inside a dog's first year, so the answers come out in weeks and months rather than years. The table below gives the full conversion for a medium dog (21 to 50 lb). Small dogs match it until 24 human years and then run slightly older; large and giant dogs run younger.
| Human years | Dog years (medium) | What that looks like |
|---|---|---|
| 1 | 0.07 (about 3 weeks) | Newborn, eyes and ears just opening |
| 3 | 0.2 (about 2.4 months) | Weaned, ready for a new home |
| 5 | 0.33 (about 4 months) | Teething, losing baby teeth |
| 10 | 0.67 (about 8 months) | Adolescent puppy |
| 15 | 1 | Young adult |
| 20 | 1.6 | Young adult |
| 24 | 2 | Fully mature |
| 30 | 3.2 | Mature adult |
| 41 | 5.4 | Mature adult |
| 50 | 7.2 | Mature adult |
| 65 | 10.2 | Senior |
| 80 | 13.2 | Geriatric |
The life stage labels follow the AAHA canine life stage guidelines, under which a medium dog is a senior for the last quarter of its 12-year average lifespan, from about age 9, and geriatric beyond 12.
What is my age in dog years?
Your age in dog years is 2 plus your human age minus 24, divided by 5, if you picture yourself as a medium dog. A 30-year-old is a 3.2-year-old dog, a 41-year-old is 5.4, and a 65-year-old is a 10.2-year-old senior. Anyone under 15 is still a puppy, and 15 to 24 is a young adult.
This is the fun way to use the calculator: type your own birthday, pick a size, and see where your life lands on a dog's timeline. Here is how a medium-dog version of a human life plays out.
- Age 10: 0.67 dog years, an 8-month-old adolescent with adult teeth and endless energy.
- Age 20: 1.6 dog years, out of puppyhood and settling into adult behavior.
- Age 30: 3.2 dog years, just past the young adult stage and entering the long mature adult plateau.
- Age 45: 6.2 dog years, a dog in its prime that has started to slow on long hikes.
- Age 65: 10.2 dog years, a senior who deserves twice-yearly vet visits.
- Age 80: 13.2 dog years, past the 12-year average lifespan for a medium dog and officially geriatric.
Choose small instead and everything shifts older, because small dogs stretch each dog year over only 4 human years. Choose giant and a 65-year-old becomes a 7.9-year-old dog that has just entered its senior stage.
Why does the reverse conversion depend on dog size?
Large dogs age faster than small dogs after age 2, so the same human age maps to fewer dog years for a Great Dane than for a Chihuahua. Human 65 equals 12.3 years for a small dog, 10.2 for a medium, 8.8 for a large and 7.9 for a giant breed. The gap widens with every human year.
A study of more than 50,000 dogs from 74 breeds by Kraus, Pavard and Promislow (2013) found that large breeds die younger mainly because they age faster, not because they start aging earlier. The size-adjusted model captures that by assigning each weight class its own rate after year 2, and the reverse calculation simply divides by that rate.
| Dog size (adult weight) | Rate after age 2 | Human 41 | Human 65 |
|---|---|---|---|
| Toy and small (under 20 lb) | 4 human years per dog year | 6.3 dog years | 12.3 dog years |
| Medium (21 to 50 lb) | 5 | 5.4 | 10.2 |
| Large (51 to 90 lb) | 6 | 4.8 | 8.8 |
| Giant (over 90 lb) | 7 | 4.4 | 7.9 |
Those rates line up with average lifespans of about 14 years for toy breeds, 13 for small, 12 for medium, 11 for large and 8.5 for giant breeds. If you do not know your dog's adult weight yet, medium is the safest default for a mixed breed of unknown parentage.
Is a dog year really 7 human years?
No. The 7-to-1 rule is a rough average that overstates puppy years and understates how fast large dogs age later in life. A dog's first year equals about 15 human years, the second adds 9, and each year after that adds 4 to 7 depending on size, according to the AVMA and AKC.
The 7-to-1 shortcut probably came from dividing a 70-year human lifespan by a 10-year dog lifespan. It is easy to remember, but it fails at both ends of a dog's life. It calls a 1-year-old dog a 7-year-old child, when that dog is already sexually mature and close to full size, more like a 15-year-old. It also calls a 10-year-old Great Dane a 70-year-old, when the size-adjusted chart puts that dog at 80 and well past its 8.5-year average lifespan.
A 2020 study by Wang and colleagues at UC San Diego compared DNA methylation in Labrador retrievers and humans and produced the formula human age = 16 × ln(dog age) + 31. It says a 1-year-old dog is epigenetically about 31, a 4-year-old about 53, and a 10-year-old about 68, which supports the idea that dogs age very quickly early and then slow down. Neither approach supports a flat 7 human years to dog years exchange rate.
Sources
- AVMA: How old is a dog in human years?
- AKC: How to calculate dog years to human years
- Kraus, Pavard and Promislow (2013), The American Naturalist: The size-life span trade-off decomposed
- Wang et al. (2020), Cell Systems: Quantitative translation of dog-to-human aging by conserved remodeling of the DNA methylome
- AAHA 2019 Canine Life Stage Guidelines
Frequently asked questions
How many dog years is 1 human year?
One human year is about 0.07 dog years, or roughly 3 weeks, for ages under 15 because a puppy reaches 15 human years by its first birthday. For an adult medium dog older than 2, one human year is one fifth of a dog year, about 10 weeks. For a giant breed it is one seventh, about 7 weeks.
How old is a 30-year-old in dog years?
A 30-year-old is about 3.2 dog years old as a medium dog, 3.5 as a small dog, 3.0 as a large dog and 2.9 as a giant breed. All four are mature adults in their prime, just past the young adult stage that ends at age 3.
How old is a 50-year-old in dog years?
A 50-year-old is 7.2 dog years old as a medium dog, 8.5 as a small dog, 6.3 as a large dog and 5.7 as a giant breed. The medium dog is still a mature adult, but the giant is only about 2 years from the start of its senior stage.
Is a 10-year-old child a puppy in dog years?
Yes. Ten human years converts to 0.67 dog years, about 8 months, which is an adolescent puppy with adult teeth that has not reached its first birthday. Every human age under 15 falls inside a dog's puppy year.
What is 100 human years in dog years?
One hundred human years equals 17.2 dog years for a medium dog, 21 for a small dog, 14.7 for a large dog and 12.9 for a giant breed. All of those ages sit beyond the average lifespan for their size, so a 100-year-old is a very old dog in any size class.
