About the GFR Calculator - Estimated Glomerular Filtration Rate
Glomerular filtration rate (GFR) measures how much blood the kidneys filter each minute, and is the standard measure of overall kidney function. Because true GFR requires a specialized clearance test, clinicians normally rely on an estimated GFR (eGFR) calculated from a routine blood test. This calculator uses the CKD-EPI 2021 creatinine equation, the race-free formula recommended by the National Kidney Foundation and American Society of Nephrology since 2021.
The CKD-EPI 2021 formula
eGFR = 142 x min(Scr / kappa, 1)^alpha x max(Scr / kappa, 1)^-1.200 x 0.9938^age, multiplied by 1.012 if the person is female. Scr is serum creatinine in mg/dL; kappa is 0.7 for females and 0.9 for males; alpha is -0.241 for females and -0.302 for males. The result is expressed in mL/min/1.73m2, standardized to an average adult body surface area.
CKD stages from the result
- G1: 90 or above - normal or high kidney function.
- G2: 60-89 - mildly decreased.
- G3a: 45-59 - mildly to moderately decreased.
- G3b: 30-44 - moderately to severely decreased.
- G4: 15-29 - severely decreased.
- G5: below 15 - kidney failure.
Putting the result in context
A stage alone does not confirm chronic kidney disease; CKD is generally defined by reduced GFR or markers of kidney damage (such as albuminuria) persisting for three months or more. A single low reading can also reflect dehydration, acute illness, or a medication effect rather than chronic disease, so results are typically confirmed with repeat testing.
When to consult a professional
This calculator performs the standard CKD-EPI arithmetic for education and tracking; it is not a diagnosis. Anyone with a result outside the normal range, or with symptoms or risk factors for kidney disease, should discuss the result and any follow-up testing with a licensed healthcare provider.