Small (20 lbs / 9 kg or less)
Medium (21-50 lbs / 10-23 kg)
Large (51-90 lbs / 24-40 kg)
Giant (Over 90 lbs / 41 kg)
Enter age and size to see results.
Understanding Your Dog's Age in Human Years
For decades, the "rule of thumb" was that one dog year equals seven human years. However, modern veterinary science suggests that this simple multiplication doesn't accurately reflect how dogs age. Different breeds and sizes age at significantly different rates, with larger dogs typically having shorter lifespans and faster physiological aging processes than smaller ones.
The Modern Formula for Dog Aging
According to the American Veterinary Medical Association (AVMA), the first year of a medium-sized dog's life is roughly equal to 15 human years. The second year of a dog's life equals about nine human years. After the second year, each additional dog year accounts for approximately four to seven human years, depending on the dog's size and breed.
Why Size Matters
Smaller dogs generally live longer than larger breeds. A 10-year-old Chihuahua is often still energetic and "middle-aged" in human terms, while a 10-year-old Great Dane is considered very elderly. This is why our calculator uses size-specific variables to give you a more accurate representation of your pet's life stage.
Size Category
Typical Weight
Aging Rate (Post Year 2)
Small
0 – 20 lbs
+4 Human Years / Year
Medium
21 – 50 lbs
+5 Human Years / Year
Large
51 – 90 lbs
+6 Human Years / Year
Giant
90+ lbs
+7 Human Years / Year
Example Calculations
Small Dog (7 years old): The first two years equal 24. The next 5 years (7 minus 2) are multiplied by 4 (20). Total = 44 human years.
Giant Dog (7 years old): The first two years equal 24. The next 5 years are multiplied by 7 (35). Total = 59 human years.
How to Keep Your Senior Dog Healthy
As your dog reaches their "senior" years (typically 7+ for most breeds), their nutritional and health needs change. Regular vet checkups, weight management, and joint supplements can help ensure they remain comfortable and active during their golden years. Monitoring their age in human years helps owners better understand the types of age-related issues to watch for, such as arthritis, vision loss, or cognitive changes.
function calculateDogAge() {
var dogAgeInput = document.getElementById('dogCurrentAge').value;
var size = document.getElementById('dogWeightCategory').value;
var resultDiv = document.getElementById('dogAgeResult');
var age = parseFloat(dogAgeInput);
if (isNaN(age) || age < 0) {
resultDiv.innerHTML = "Please enter a valid age (0 or higher).";
return;
}
var humanYears = 0;
if (age === 0) {
humanYears = 0;
} else if (age > 0 && age 1 && age <= 2) {
// Linear interpolation for the second year (15 to 24)
humanYears = 15 + ((age – 1) * 9);
} else {
// Base 24 years for the first two years
var baseAge = 24;
var multiplier = 4; // Default for small
if (size === 'medium') {
multiplier = 5;
} else if (size === 'large') {
multiplier = 6;
} else if (size === 'giant') {
multiplier = 7;
}
humanYears = baseAge + ((age – 2) * multiplier);
}
// Rounding to 1 decimal place for clarity if they use partial years
var finalResult = Math.round(humanYears * 10) / 10;
var lifeStage = "";
if (humanYears < 12) lifeStage = " (Puppy)";
else if (humanYears < 25) lifeStage = " (Young Adult)";
else if (humanYears < 50) lifeStage = " (Adult)";
else if (humanYears < 70) lifeStage = " (Senior)";
else lifeStage = " (Geriatric)";
resultDiv.innerHTML = "Your dog is approximately " + finalResult + " human years old." + lifeStage;
}