GFR Calculator - Estimated Glomerular Filtration Rate | Free Online Kidney Function Tool

Estimated glomerular filtration rate, usually shortened to eGFR, is one of the most widely used markers of kidney function. It is not measured directly in everyday practice. Instead, clinicians estimate it from serum creatinine, age, and sex, then interpret the result alongside urine findings, symptoms, blood pressure, medications, and the overall clinical picture. A single eGFR value can help screen for chronic kidney disease, monitor the effect of diabetes or hypertension on the kidneys, and guide medication dosing decisions. This calculator brings together three of the most common equations so you can compare them in one place. The primary result shown here is CKD-EPI 2021, the newer race-free equation that many laboratories and guidelines now prefer. It adjusts the calculation slightly for sex because average creatinine production differs with muscle mass patterns, and it accounts for the normal age-related decline in kidney filtration. In general, CKD-EPI performs better than older equations when kidney function is near normal, which is why it has become the default in many clinical settings. The stage label in the result panel is linked to this value because modern CKD staging usually starts with the best available eGFR estimate. The MDRD equation is included because it remains familiar to many clinicians and may still appear in older lab reports, published research, or legacy electronic records. MDRD includes the historical African American coefficient that used to be applied in some settings. That coefficient is now controversial and no longer used in the newer CKD-EPI 2021 equation, but it remains relevant if you are comparing against older literature or systems that still calculate MDRD in its traditional form. This tool does not recommend one social or biological interpretation of race; it simply reproduces the classic formula for transparency and comparison. Cockcroft-Gault estimates creatinine clearance rather than normalized GFR and requires body weight, so it is especially useful when a drug monograph or dosing protocol still calls for it. Because it is not normalized to a body surface area of 1.73 square meters, its units are shown separately as mL/min. Optional height is included so the tool can provide BMI context when both weight and height are entered, but height is not part of the GFR formulas listed here. That makes the input panel practical for clinicians who want a quick body-size check while reviewing kidney estimates. The staging bands displayed follow the usual chronic kidney disease categories: G1 is 90 or higher, G2 is 60 to 89, G3a is 45 to 59, G3b is 30 to 44, G4 is 15 to 29, and G5 is below 15. Those categories matter most when a reduced GFR persists for at least three months or when there is other evidence of kidney damage such as albuminuria. A one-time result can be affected by dehydration, acute illness, unusual muscle mass, supplements, or lab variation. Use this calculator for education and preliminary review, but rely on a clinician for diagnosis, trend interpretation, and treatment decisions.