This calculator is for educational purposes only. It does not provide medical advice. Consult a healthcare professional for diagnosis.
function calculateGFR() {
var scr = parseFloat(document.getElementById('scr').value);
var age = parseInt(document.getElementById('age').value);
var isFemale = document.getElementById('genderFemale').checked;
if (isNaN(scr) || isNaN(age) || scr <= 0 || age = 90) {
stageText = "Stage 1";
stageClass = "bg-green";
interpText = "Normal or high kidney function. Kidney damage may be present if other signs (like protein in urine) are detected.";
} else if (egfr >= 60) {
stageText = "Stage 2";
stageClass = "bg-green"; // Still generally considered 'green' unless issues present, but technically mild decrease
interpText = "Mildly decreased kidney function.";
} else if (egfr >= 45) {
stageText = "Stage 3a";
stageClass = "bg-yellow";
interpText = "Mild to moderately decreased kidney function.";
} else if (egfr >= 30) {
stageText = "Stage 3b";
stageClass = "bg-orange";
interpText = "Moderate to severely decreased kidney function.";
} else if (egfr >= 15) {
stageText = "Stage 4";
stageClass = "bg-red";
interpText = "Severely decreased kidney function.";
} else {
stageText = "Stage 5";
stageClass = "bg-darkred";
interpText = "Kidney failure (End Stage Renal Disease).";
}
var badge = document.getElementById('ckdStage');
badge.innerText = stageText;
badge.className = "stage-badge " + stageClass;
document.getElementById('interpretation').innerText = interpText;
}
What is GFR?
Glomerular Filtration Rate (GFR) is widely considered the best overall index of kidney function. In simple terms, it measures how much blood your kidneys filter each minute. Your kidneys contain tiny filters called glomeruli that remove waste and excess fluid from the blood.
Because measuring GFR directly involves complex procedures, medical professionals usually estimate it (eGFR) using a blood test for creatinine—a waste product created by normal muscle breakdown. This calculator uses the CKD-EPI 2021 (Race-Free) equation, which is currently recommended by the National Kidney Foundation and the American Society of Nephrology.
How the Calculation Works
The calculation of GFR rate relies on several key physiological variables:
Serum Creatinine: High levels of creatinine in the blood indicate that the kidneys are not filtering waste efficiently.
Age: Kidney function naturally declines slightly as we age.
Gender: Muscle mass differs between biological males and females, which affects creatinine generation.
The standard formula outputs a number representing milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²).
Understanding the 5 Stages of Chronic Kidney Disease (CKD)
Your GFR result helps determine the stage of kidney disease:
Stage 1 (GFR > 90): Normal or high function. Kidney damage may be present (e.g., protein in urine), but filtration is efficient.
Stage 2 (GFR 60-89): Mildly decreased function. Observation is usually required to monitor trends.
Stage 3a (GFR 45-59): Mild to moderate decrease. This is often where medical intervention begins to preserve remaining function.
Stage 3b (GFR 30-44): Moderate to severe decrease. Increased risk of complications.
Stage 4 (GFR 15-29): Severely decreased function. Preparation for kidney replacement therapy (dialysis or transplant) often begins here.
Stage 5 (GFR < 15): Kidney failure. Dialysis or transplant is necessary to maintain life.
Why Use the CKD-EPI 2021 Equation?
In 2021, the task force of the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended a new equation that calculates eGFR without a race coefficient. Previous versions (like the 2009 equation) adjusted results based on race (specifically for Black individuals), based on the assumption of higher muscle mass. The new 2021 equation removes this variable to ensure equitable diagnosis and treatment for all patients.
When Should You Calculate Your GFR?
You should consult a doctor about your GFR if you have risk factors for kidney disease, including: