Convert your dog's years into human years using precise biological aging science.
Small (20 lbs or less)
Medium (21-50 lbs)
Large (51-90 lbs)
Giant (Over 90 lbs)
How Old is My Dog in Human Years?
The old "one dog year equals seven human years" rule is a popular myth. Modern veterinary science suggests that dogs age much more rapidly during their first two years of life, and their aging process slows down or varies significantly based on their breed and physical size.
The Science of Dog Aging
A one-year-old dog is generally considered equivalent to a 15-year-old human. By their second birthday, they have reached the equivalent of a 24-year-old human. From that point forward, the rate of aging depends on the dog's size. Larger breeds tend to have shorter lifespans and age faster as they reach senior status compared to smaller breeds.
Dog Age
Small Dog
Medium Dog
Large Dog
Giant Dog
1 Year
15 Years
15 Years
15 Years
15 Years
2 Years
24 Years
24 Years
24 Years
24 Years
5 Years
36 Years
37 Years
40 Years
42 Years
10 Years
56 Years
60 Years
66 Years
78 Years
Why Do Larger Dogs Age Faster?
While most mammals follow the rule that larger species live longer (like elephants vs. mice), domestic dogs are an anomaly. Scientists believe that because large breeds grow from puppyhood to massive adult sizes so quickly, it causes high levels of oxidative stress and rapid cell division, leading to age-related diseases earlier in life.
Signs Your Dog is Entering Senior Years
Cloudy Eyes: A common sign of aging, though it should be checked for cataracts.
Reduced Activity: Taking longer to get up or slowing down on walks.
Graying Fur: Usually starts around the muzzle and eyes.
Weight Changes: Metabolism slows down, making weight gain easier.
function calculateDogAge() {
var dogAgeInput = document.getElementById('dogAge').value;
var dogSize = document.getElementById('dogSize').value;
var resultDiv = document.getElementById('dogResult');
var dogAge = parseFloat(dogAgeInput);
var humanAge = 0;
if (isNaN(dogAge) || dogAge < 0) {
resultDiv.style.display = "block";
resultDiv.innerHTML = "Please enter a valid age for your dog.";
resultDiv.style.backgroundColor = "#fee2e2";
resultDiv.style.borderLeftColor = "#ef4444";
return;
}
// Standard styling for valid result
resultDiv.style.backgroundColor = "#e8f4fd";
resultDiv.style.borderLeftColor = "#3498db";
if (dogAge === 0) {
humanAge = 0;
} else if (dogAge <= 1) {
// First year is roughly 15 human years
humanAge = dogAge * 15;
} else if (dogAge <= 2) {
// Second year adds about 9 human years (Total 24)
humanAge = 15 + ((dogAge – 1) * 9);
} else {
// Base age after 2 years is 24
humanAge = 24;
var remainingYears = dogAge – 2;
if (dogSize === "small") {
humanAge += (remainingYears * 4);
} else if (dogSize === "medium") {
humanAge += (remainingYears * 5);
} else if (dogSize === "large") {
humanAge += (remainingYears * 6);
} else if (dogSize === "giant") {
humanAge += (remainingYears * 8);
}
}
resultDiv.style.display = "block";
resultDiv.innerHTML = "A " + dogAge + " year old " + dogSize + " dog is approximately " + humanAge.toFixed(1) + " human years old!";
}