Dog Age Calculator

1. Enter your dog's age in years. Use decimals for partial years. A 6-month-old dog is 0.5 years. The calculator accepts ages from 6 months up to 25 years.
2. Select your dog's size category. Size matters more than breed for aging rate. Small dogs (under 20 lbs) age more slowly than giant breeds (over 90 lbs), which is why Great Danes rarely live past 10 while Chihuahuas often reach 15 to 18 years.
3. Read the human equivalent age. A 5-year-old medium dog is roughly equivalent to a 36-year-old human. The same dog at size "giant" would be closer to 36 as well, but differences become dramatic by age 8 to 10.
4. Check the life stage. Life stage (Puppy, Adolescent, Adult, Mature Adult, Senior) helps you understand what health and behavioral changes to expect.
5. Browse the full comparison table. The table below the calculator shows human equivalents for dog ages 1 through 20 for your selected size class.

The old "multiply by 7" formula is inaccurate for two reasons. First, dogs reach sexual maturity at about 12 months, which is more like a 15-year-old human. Second, large and giant breeds age considerably faster than small breeds in their middle and senior years.

This calculator uses a year-by-year conversion table based on comparative physiology research and American Veterinary Medical Association guidelines. Key milestones:

The divergence after age 5 is striking. A 10-year-old small dog is like a 56-year-old human, while a 10-year-old giant breed is like a 79-year-old. This explains why small dogs consistently outlive large breeds: their slower aging rate means less cellular damage over time.

A 2020 study in Cell Systems used DNA methylation (epigenetic aging markers) to propose that dog age in human years can be estimated as: 16 × ln(dog age) + 31. This formula applies to Labrador Retrievers specifically. The table-based approach used here is better for comparing across size classes.