Medical & Pharmaceutical
GFR Calculator
Calculate estimated Glomerular Filtration Rate (eGFR) to assess kidney function and determine chronic kidney disease stages.
Reviewed by the calculator.uk.com Team · Last reviewed 22 May 2026 · Our methodology
Enter values to calculate estimated GFR
Related to GFR Calculator
The Glomerular Filtration Rate (GFR) Calculator estimates how well your kidneys filter waste from the blood, using serum creatinine along with age, sex, and race. Because directly measuring true GFR requires clearance testing with an exogenous filtration marker, clinicians instead rely on validated regression equations that estimate GFR (eGFR) from a routine blood test. This calculator supports the two most widely used equations: the MDRD Study equation and the CKD-EPI creatinine equation.
The MDRD Study Equation
The Modification of Diet in Renal Disease (MDRD) equation calculates eGFR as 175 × (serum creatinine)⁻¹·¹⁵⁴ × (age)⁻⁰·²⁰³, multiplied by 0.742 for women and 1.212 for Black patients. It was derived from a cohort of patients with existing kidney disease, which makes it more accurate at lower GFR values but less reliable for people with normal or near-normal kidney function.
The CKD-EPI Equation
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2009 creatinine equation uses a two-slope model that adjusts differently depending on whether creatinine is above or below a sex-specific threshold (kappa), combined with an exponent (alpha) and an age-decay term. It was developed from a broader, healthier population than the MDRD cohort, so it performs more accurately across the full range of kidney function and is now the equation generally preferred in clinical practice.
The calculator returns your estimated GFR in mL/min/1.73m², a unit that normalizes filtration rate to a standard body surface area so results can be compared across individuals. It then maps that value onto the five-stage chronic kidney disease (CKD) classification used in clinical guidelines.
CKD Stages by eGFR
Stage 1 (eGFR ≥ 90) is normal or high function; Stage 2 (60–89) is mildly decreased; Stage 3a (45–59) is mild to moderately decreased; Stage 3b (30–44) is moderately to severely decreased; Stage 4 (15–29) is severely decreased; and Stage 5 (below 15) indicates kidney failure. Stages 1 and 2 are only classified as CKD when accompanied by other markers of kidney damage, such as protein in the urine.
eGFR is an estimate, not a direct measurement, and it can be thrown off by factors unrelated to kidney function, including muscle mass, recent high-intake meat consumption, pregnancy, and rapidly changing kidney function in acute illness. A single low reading is not a diagnosis; CKD is typically confirmed when reduced eGFR or other markers of kidney damage persist for at least three months, and any concerning result should be discussed with a healthcare provider.
1. What is the difference between the MDRD and CKD-EPI equations?
Both estimate GFR from serum creatinine, age, sex, and race, but they were built from different patient populations. MDRD was derived mainly from people with reduced kidney function, so it tends to underestimate GFR in healthier individuals. CKD-EPI was developed from a larger and healthier population and is generally more accurate across the full range of kidney function, which is why most laboratories now report CKD-EPI by default.
2. Why does the calculator ask about race?
The original MDRD and 2009 CKD-EPI equations included a coefficient for Black race because early validation studies observed, on average, higher measured GFR at a given creatinine level in that population, likely reflecting differences in average muscle mass rather than kidney physiology itself. Because of concerns that a race-based adjustment can bias care, kidney health organizations in the United States now recommend a race-free version of the CKD-EPI equation (2021) for clinical use. This calculator implements the original race-inclusive 1999 MDRD and 2009 CKD-EPI formulas for reference and comparison, so results may differ from a race-free calculation.
3. Can this calculator diagnose chronic kidney disease?
No. It provides an estimate that clinicians use as one input alongside a urine albumin-to-creatinine ratio, blood pressure, imaging, and a patient's full medical history. A diagnosis of CKD generally requires reduced eGFR or other evidence of kidney damage to persist for three months or longer, and it should always be made by a qualified healthcare professional.
4. What factors can affect the accuracy of estimated GFR?
Serum creatinine, and therefore eGFR, is influenced by muscle mass, age, diet, hydration status, certain medications, and rapid changes in kidney function during acute illness. People with unusually high or low muscle mass (such as bodybuilders, amputees, or those with muscle-wasting conditions) may get eGFR values that don't reflect their true kidney function, and in those cases a cystatin C-based equation or a direct clearance test is more reliable.
5. What is the scientific source for this calculator?
The MDRD coefficients used here come from Levey and colleagues' 1999 paper in Annals of Internal Medicine that introduced the equation, while the CKD-EPI formula comes from the same group's 2009 follow-up in that journal, developed to correct MDRD's tendency to underestimate filtration in healthier kidneys. The stage cutoffs used to classify results, at 90, 60, 45, 30 and 15 mL/min/1.73m², match the KDIGO 2012 clinical practice guideline for chronic kidney disease, the framework nephrologists use worldwide to stage disease severity.