Kidney Function Calculator (eGFR)
Estimates your glomerular filtration rate (eGFR) using the CKD-EPI equation from serum creatinine, age, sex, and race. Clinicians and patients use it to stage chronic kidney disease and track how well the kidneys are filtering blood.
About this calculator
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation estimates GFR in mL/min/1.73 m² from serum creatinine. It uses different exponents depending on whether creatinine is below or above a sex-specific threshold (κ = 0.7 for females, 0.9 for males): eGFR = 141 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.209 × 0.993^Age × [1.018 if female] × [1.159 if Black]. Here α is −0.329 for females and −0.411 for males. The 0.993^Age term captures the natural annual decline in kidney function with age. The race multiplier was derived from observed differences in creatinine generation due to muscle mass; however, many institutions are moving away from race-based adjustments, so clinical context matters. An eGFR ≥ 60 is generally considered normal; values below 15 indicate kidney failure.
How to use
Example: a 55-year-old Black female with serum creatinine of 1.1 mg/dL. Step 1: κ = 0.7 (female). Scr/κ = 1.1/0.7 = 1.571. Step 2: min(1.571, 1) = 1, so first term = 141 × 1^(−0.329) = 141. Step 3: max(1.571, 1) = 1.571, so second term = 1.571^(−1.209) ≈ 0.596. Step 4: Age term = 0.993^55 ≈ 0.681. Step 5: Apply multipliers: 141 × 0.596 × 0.681 × 1.018 × 1.159 ≈ 65.7 mL/min/1.73 m². This falls in CKD Stage G2 (mildly reduced).
Frequently asked questions
What is a normal eGFR value and what do low results mean for kidney health?
An eGFR of 90 or above is considered normal kidney function. Values between 60 and 89 suggest mildly reduced function (Stage G2), which may simply reflect age-related decline. An eGFR between 30 and 59 indicates moderately reduced function (Stages G3a/G3b) and warrants monitoring by a nephrologist. Below 15 mL/min/1.73 m² indicates kidney failure, at which point dialysis or transplantation may be considered. A single low reading should always be confirmed with a repeat test, as acute illness can temporarily lower eGFR.
How does serum creatinine relate to kidney function in the GFR calculation?
Creatinine is a metabolic waste product produced at a relatively constant rate by muscle tissue and filtered almost exclusively by the glomeruli of the kidneys. When kidney filtration declines, creatinine accumulates in the blood, so higher serum creatinine correlates with lower GFR. The CKD-EPI equation accounts for the non-linear relationship between creatinine and GFR, using different mathematical exponents for values below and above sex-specific thresholds. This makes it more accurate than the older MDRD equation across a wider range of kidney function levels, especially in people with normal or near-normal GFR.
Why does the CKD-EPI formula include race as a variable and is that still used today?
The original CKD-EPI 2009 equation included a multiplier for patients identified as Black or African American based on observed differences in average serum creatinine levels, attributed to higher average muscle mass in that population. However, race is a social construct rather than a biological variable, and using it in clinical equations can perpetuate health disparities. In 2021, the National Kidney Foundation and American Society of Nephrology recommended transitioning to the race-free CKD-EPI 2021 equation, which uses cystatin C alongside creatinine. Many hospitals have already adopted the updated formula, so check which version your clinician is using.