Convert your pet rat's age to human equivalent years
Equivalent Human Age:
Understanding Rat Aging: How Old is Your Rat in Human Years?
Rats have a remarkably fast metabolism and a relatively short lifespan compared to humans. While a domestic "fancy rat" typically lives between 2 and 3 years, they progress through life stages at an accelerated rate. Understanding where your rat sits on the human age spectrum helps in providing age-appropriate care, nutrition, and veterinary attention.
The Rat-to-Human Age Conversion Formula
Calculating a rat's age isn't as simple as multiplying by a fixed number. Because rats mature sexually within weeks of birth, their early development is much faster than human development. Generally, the first few months of a rat's life represent a massive leap in "human years," while the pace slows slightly as they enter adulthood.
Infancy: 0 to 3 weeks. By 3 weeks, a rat is equivalent to a human toddler.
Puberty: Around 6 weeks. At this stage, a rat is roughly 12.5 human years old.
Adulthood: 6 months. A 6-month-old rat is physically comparable to an 18-year-old human.
Middle Age: 12 months. At one year old, a rat is approximately 38 human years old.
Senior Years: 24 months. A two-year-old rat is equivalent to a 70-year-old human.
Rat to Human Age Conversion Table
Rat Age
Human Equivalent
Life Stage
1.5 Months (6 Weeks)
12.5 Years
Puberty / Teenager
6 Months
18 Years
Young Adult
12 Months (1 Year)
38 Years
Middle-Aged Adult
18 Months (1.5 Years)
54 Years
Mature Adult
24 Months (2 Years)
70 Years
Senior
30 Months (2.5 Years)
85 Years
Geriatric
36 Months (3 Years)
100 Years
Centenarian
Example Calculations
Example 1: If your rat is 4 months old, the calculator determines they are approximately 15.5 human years old. They are effectively a high-school-aged teenager, full of energy and still growing.
Example 2: A rat that has reached 22 months is equivalent to a human in their mid-60s. This is the stage where you might notice more sleeping, slight weight loss, or the onset of age-related mobility issues like Hind Leg Degeneration (HLD).
Health Care for Aging Rats
As your rat enters their "50s" (around 16-18 months), keep an eye out for common health issues such as respiratory infections, tumors (especially in females), and kidney function decline. Providing a diet lower in protein and phosphorus can help support their aging kidneys, while ensuring their cage layout is accessible (fewer steep ramps) helps seniors with stiff joints.
function calculateRatAge() {
var months = parseFloat(document.getElementById('ratMonths').value) || 0;
var weeks = parseFloat(document.getElementById('ratWeeks').value) || 0;
// Convert all to months (approx 4.345 weeks per month)
var totalMonths = months + (weeks / 4.345);
var humanYears = 0;
var lifeStage = "";
if (totalMonths <= 0) {
humanYears = 0;
lifeStage = "Newborn";
} else if (totalMonths <= 1.5) {
// Birth to Puberty (6 weeks = 12.5 human years)
humanYears = totalMonths * (12.5 / 1.5);
lifeStage = "Juvenile (Infancy to Puberty)";
} else if (totalMonths <= 6) {
// Puberty to Young Adult (6 months = 18 human years)
humanYears = 12.5 + (totalMonths – 1.5) * ((18 – 12.5) / (6 – 1.5));
lifeStage = "Teenager / Adolescent";
} else if (totalMonths <= 12) {
// Young Adult to Middle Age (12 months = 38 human years)
humanYears = 18 + (totalMonths – 6) * ((38 – 18) / (12 – 6));
lifeStage = "Prime Adulthood";
} else if (totalMonths <= 24) {
// Middle Age to Senior (24 months = 70 human years)
humanYears = 38 + (totalMonths – 12) * ((70 – 38) / (24 – 12));
lifeStage = "Mature Adult to Senior";
} else if (totalMonths <= 36) {
// Senior to Geriatric (36 months = 100 human years)
humanYears = 70 + (totalMonths – 24) * ((100 – 70) / (36 – 24));
lifeStage = "Geriatric / Very Old";
} else {
// Beyond 3 years
humanYears = 100 + (totalMonths – 36) * 2.5;
lifeStage = "Extremely Long-Lived";
}
var resultDiv = document.getElementById('ratResult');
var ageDisplay = document.getElementById('humanAgeDisplay');
var stageDisplay = document.getElementById('lifeStageDisplay');
ageDisplay.innerHTML = humanYears.toFixed(1) + " Human Years";
stageDisplay.innerHTML = "Current Life Stage: " + lifeStage;
resultDiv.style.display = "block";
}