GFR Calculator

The estimated Glomerular Filtration Rate (eGFR) is the main measure doctors use to gauge how well your kidneys are working. It estimates how much blood your kidneys filter each minute, expressed in mL/min/1.73m² of body surface area. This calculator uses the CKD-EPI 2021 equation, the race-free formula now recommended by major nephrology bodies, and maps your result onto the standard six-stage chronic kidney disease (CKD) scale so you can see roughly where you fall. It is a quick screening and educational aid, not a diagnosis.

Not medical advice. This tool is for general information and self-tracking only. An eGFR figure cannot diagnose kidney disease on its own, and a single reading can be misleading. Only a qualified doctor can interpret your kidney function in the context of your full history, urine tests, blood pressure and repeat results. Always consult a physician or nephrologist before drawing any conclusion or changing medication, diet or lifestyle.

Who this calculator is for

It is useful if you have recently had a blood test that reported serum creatinine and want to understand what the number suggests, if you live with diabetes or high blood pressure and want to keep an eye on kidney health between check-ups, or if you simply want to learn how eGFR and CKD staging work. It is not a substitute for a clinical review, and people who are pregnant, very muscular, on dialysis, or have rapidly changing creatinine should rely on their doctor's assessment rather than any online estimate.

The CKD-EPI 2021 formula

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2021 equation was revised to drop race as a variable, making estimates fairer across populations. It combines serum creatinine, age and sex: eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × (1.012 if female), where κ is 0.7 for females and 0.9 for males, and α is −0.241 for females and −0.302 for males. The Cockcroft-Gault equation is an older alternative that estimates creatinine clearance and additionally needs body weight; it is still used for some drug-dosing decisions, but CKD-EPI is the modern standard for reporting eGFR.

Understanding CKD staging

Chronic kidney disease is graded in six stages from G1 to G5 based on the eGFR value: G1 is 90 or above (normal or high), G2 is 60–89 (mildly decreased), G3a is 45–59, G3b is 30–44, G4 is 15–29 (severely decreased) and G5 is below 15 (kidney failure). Staging helps doctors decide on monitoring frequency, adjust medication doses, and plan ahead for treatments such as dialysis when needed. An eGFR above 60 is generally regarded as the normal-to-mild range, and a mild drop is common and often harmless with increasing age.

Worked example

Take a 45-year-old man with a serum creatinine of 1.0 mg/dL. Here κ = 0.9, so Scr/κ = 1.11; since that is above 1, the min term is 1 and the max term is 1.11. The calculation becomes 142 × 1 × 1.11^−1.200 × 0.9938^45, which works out to an eGFR of roughly 95 mL/min/1.73m², placing him in stage G1 (normal). If creatinine rose to 1.6 mg/dL with everything else unchanged, the eGFR would fall to around 54, which corresponds to stage G3a and would warrant a conversation with a doctor and a repeat test.

Tips and common mistakes

• Use the serum creatinine value in mg/dL exactly as printed on your lab report; using the wrong unit throws the result off completely.
• CKD is defined by an eGFR that stays below 60 for at least three months, so never treat one low reading as a diagnosis.
• Stay normally hydrated before a creatinine test, since dehydration can temporarily raise creatinine and lower the estimate.
• Very muscular people and bodybuilders may show a lower eGFR than their true kidney function because creatinine reflects muscle mass.
• Remember the formula assumes stable kidney function; it is unreliable during acute illness or rapidly changing creatinine.