Kidney Function Calculator (eGFR)
Estimates your glomerular filtration rate (eGFR) using the race-free CKD-EPI 2021 creatinine equation from serum creatinine, age and sex. Clinicians and patients use it to stage chronic kidney disease and track how well the kidneys are filtering blood.
Last updated: September 2026
Formula below · 3 sources (niddk.nih.gov, CDC, Wikipedia) · Updated Sep 2026
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About this calculator
The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2021 creatinine equation estimates GFR in mL/min/1.73 m² from serum creatinine, age and sex, and is the equation recommended by the NKF-ASN Task Force (2021) for US laboratories. 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 = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^Age × [1.012 if female]. Here α is −0.241 for females and −0.302 for males. The 0.9938^Age term captures the natural decline in kidney function with age. Unlike the 2009 CKD-EPI and the MDRD equations, the 2021 equation has no race coefficient. Enter creatinine in mg/dL (divide µmol/L by 88.4). An eGFR of 90 or more is normal, 60–89 mildly reduced, 30–59 moderately reduced (CKD G3), 15–29 severely reduced (G4), and below 15 kidney failure (G5); CKD requires the reduction or other kidney damage to persist for at least 3 months.
How to use
Example: a 55-year-old woman 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 the first term = 142 × 1^(−0.241) = 142. Step 3: max(1.571, 1) = 1.571, so the second term = 1.571^(−1.200) ≈ 0.5814. Step 4: age term = 0.9938^55 ≈ 0.7103. Step 5: multiply and apply the female factor: 142 × 0.5814 × 0.7103 × 1.012 ≈ 59.3 mL/min/1.73 m². This falls just inside CKD stage G3a (45–59, moderately reduced) and would need to persist for 3 months to diagnose CKD. A 55-year-old man with creatinine 1.2 mg/dL gets 71.4 (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 did the CKD-EPI formula include race, 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, refit without a race term; it has a creatinine-only version (used here) and a version that adds cystatin C for confirmation. Most US laboratories now report the 2021 equation, and this calculator does not ask for race.