Estimate kidney function using the race-free CKD-EPI equation
Your Estimated GFR:
—
Stage: —
function calculateGFR() {
var scr = parseFloat(document.getElementById('creatinine').value);
var age = parseInt(document.getElementById('age').value);
var sex = document.querySelector('input[name="sex"]:checked').value;
var resultBox = document.getElementById('gfr-result-box');
var gfrValue = document.getElementById('gfr-value');
var gfrStage = document.getElementById('gfr-stage');
var gfrDesc = document.getElementById('gfr-description');
if (isNaN(scr) || isNaN(age) || scr <= 0 || age <= 0) {
alert('Please enter valid positive numbers for Creatinine and Age.');
return;
}
var k, alpha, genderMultiplier;
if (sex === 'female') {
k = 0.7;
alpha = -0.241;
genderMultiplier = 1.012;
} else {
k = 0.9;
alpha = -0.302;
genderMultiplier = 1.0;
}
// CKD-EPI 2021 Equation:
// 142 * min(Scr/k, 1)^alpha * max(Scr/k, 1)^-1.200 * 0.9938^age * (1.012 if female)
var minVal = Math.min(scr / k, 1);
var maxVal = Math.max(scr / k, 1);
var egfr = 142 * Math.pow(minVal, alpha) * Math.pow(maxVal, -1.200) * Math.pow(0.9938, age) * genderMultiplier;
var roundedGFR = Math.round(egfr);
gfrValue.innerHTML = roundedGFR + " mL/min/1.73 m²";
var stage = "";
var desc = "";
var color = "";
if (roundedGFR >= 90) {
stage = "G1 (Normal or High)";
desc = "Kidney function is normal, but other signs of kidney disease may be present.";
color = "#28a745";
} else if (roundedGFR >= 60) {
stage = "G2 (Mildly Decreased)";
desc = "Mild loss of kidney function. Often monitored if other risk factors exist.";
color = "#8bc34a";
} else if (roundedGFR >= 45) {
stage = "G3a (Mildly to Moderately Decreased)";
desc = "Mild to moderate loss of kidney function. Clinical evaluation is usually recommended.";
color = "#ffc107";
} else if (roundedGFR >= 30) {
stage = "G3b (Moderately to Severely Decreased)";
desc = "Moderate to severe loss of kidney function. Increased risk of complications.";
color = "#fd7e14";
} else if (roundedGFR >= 15) {
stage = "G4 (Severely Decreased)";
desc = "Severe loss of kidney function. Preparation for kidney replacement therapy may be necessary.";
color = "#d9534f";
} else {
stage = "G5 (Kidney Failure)";
desc = "End-stage renal disease (ESRD). Dialysis or transplant is typically required.";
color = "#c82333";
}
gfrStage.innerText = stage;
gfrStage.style.color = color;
gfrDesc.innerText = desc;
resultBox.style.display = 'block';
resultBox.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}
How is Glomerular Filtration Rate (GFR) Calculated?
Glomerular Filtration Rate (GFR) is the primary metric used by medical professionals to determine how well your kidneys are filtering waste from your blood. Because direct measurement of GFR is complex and requires specialized equipment, clinicians use equations to provide an estimated GFR (eGFR).
The Modern CKD-EPI 2021 Formula
Historically, GFR calculations included race as a variable. However, in 2021, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended the adoption of the race-free CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. This calculator uses that specific formula:
Serum Creatinine (Scr): A waste product from muscle breakdown. Higher levels in the blood usually indicate lower kidney function.
κ (Kappa): 0.7 for females and 0.9 for males.
α (Alpha): -0.241 for females and -0.302 for males.
Age: Kidney function naturally declines as we get older, which the formula accounts for.
What Does Your Result Mean?
A "normal" GFR for adults is typically 90 mL/min/1.73 m² or higher. However, GFR can be affected by pregnancy, muscle mass, and acute illness. Below is a general guide to the stages of Chronic Kidney Disease (CKD):
eGFR Level
CKD Stage
Interpretation
90+
Stage 1
Normal function
60-89
Stage 2
Mildly decreased
30-59
Stage 3
Moderate decrease
15-29
Stage 4
Severe decrease
< 15
Stage 5
Kidney Failure
Disclaimer: This calculator is for educational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider regarding kidney health.