Tinker 
How to use the dog age calculator
Type your dog's age in whole years, then add any extra months (0 to 11). Pick the size your dog is or will be as an adult: small up to 20 lb (9 kg), medium 21–50 lb (9.5–23 kg), large 51–100 lb (23–45 kg) or giant over 100 lb (45 kg). For mixed breeds, go by weight rather than breed.
The main result is the size-based chart estimate. Below it you'll see the DNA-based estimate and a life stage label, so you can compare the two approaches.
The formulas in plain words
The old "multiply by 7" rule is too simple. Dogs grow up very fast and then age more slowly. The size chart used here follows the widely cited veterinary pattern: the first year of a dog's life equals about 15 human years, the second year adds about 9 more (24 in total), and each year after that adds 4 years for small dogs, 5 for medium, 6 for large and 7 for giant breeds. Bigger dogs age faster in later life, which is why their rate is higher. Ages under one year are scaled in proportion, so a 6-month-old puppy is about 7.5.
The DNA-based estimate comes from a 2019 study that compared chemical changes in DNA (methylation) in Labrador retrievers and people. Its formula is human age = 16 × ln(dog age) + 31, where ln is the natural logarithm. It suggests young dogs are "older" than charts imply and that ageing slows later. It was built on one breed, so treat it as an interesting second opinion.
Worked example
A 5-year-old medium dog: the first two years count as 24 human years. The remaining 3 years at 5 per year add 15, giving 24 + 15 = 39 human years, which puts the dog in the Adult stage.
With the DNA formula: ln(5) ≈ 1.6094, so 16 × 1.6094 + 31 ≈ 56.8 human years. The gap between 39 and 56.8 shows how differently the two methods treat middle age.
Tips and limits
These are estimates for fun and general understanding, not a health assessment. Genetics, diet, weight and care all affect how a particular dog ages, and many small breeds live well past 15 while giant breeds often have shorter lives.
Life stages here are based on the human-equivalent age: Puppy under 13, Adolescent 13–19, Adult 20–49, Mature adult 50–69 and Senior 70 or more. Many vets suggest twice-yearly check-ups once a dog reaches its senior years, which comes earlier for large and giant dogs.
Frequently asked questions
Is one dog year really seven human years?
No. That rule is a rough average. Dogs mature much faster in their first two years (about 24 human years by age two) and then age at roughly 4 to 7 human years per year depending on size.
Why do large dogs age faster than small dogs?
Larger breeds reach adulthood on a similar timeline but tend to develop age-related problems sooner and have shorter average lifespans, so each later year counts for more human years.
Which result should I trust, the chart or the DNA formula?
Both are estimates. The size chart reflects common veterinary guidance and accounts for size; the DNA formula is newer science but was based on Labradors only. Many people use the chart and see the DNA figure as a curiosity.
How old is a 1-year-old dog in human years?
About 15 human years on the size chart, roughly a teenager. The DNA-based formula gives about 31, because ln(1) is zero.