NKF GFR Calculator
The NKF GFR Calculator estimates your glomerular filtration rate (eGFR) based on serum creatinine, age, sex, and race. This tool helps adults quickly assess kidney function to detect potential signs of chronic kidney disease (CKD). Whether you are monitoring a specific condition or reviewing routine blood work, this calculator provides immediate medical staging based on the 2009 CKD-EPI creatinine equation.
The glomerular filtration rate (GFR) is a measure of how well your kidneys are filtering waste from your blood. While a direct measurement requires complex procedures, the estimated GFR (eGFR) provides a useful approximation using a simple blood test for creatinine. This calculation is critical for early detection and management of chronic kidney disease (CKD).
How eGFR Is Calculated
eGFR = 141 × min(Scr/k, 1)^a × max(Scr/k, 1)^-1.209 × 0.993^Age × SexFactor × RaceFactor
Where:
- Scr = Serum creatinine (mg/dL)
- k = Sex-specific constant (0.9 for men, 0.7 for women)
- a = Sex-specific exponent (-0.411 for men, -0.329 for women)
- Age = Patient's age in years
- SexFactor = 1.018 if female, 1.0 if male
- RaceFactor = 1.159 if Black, 1.0 if Non-Black
The calculation adjusts creatinine levels based on age and muscle mass (implied by sex and race). As we age, our GFR naturally declines. The formula accounts for this by applying an age factor of 0.993 for every year of life. The National Kidney Foundation recommends the CKD-EPI (2009) equation as the standard for adults because it is better-informed than older methods, especially when kidney function is only mildly reduced.
What Your eGFR Means
Your eGFR number provides information to helpr healthcare provider determine the stage of kidney disease, if any. A "normal" eGFR is typically 60 or higher, but the estimated number helps categorize the severity of damage.
Understanding the Stages
- Stage G1 (eGFR ≥ 90): Normal kidney function with no signs of damage.
- Stage G2 (eGFR 60–89): Mildly decreased kidney function.
- Stage G3a (eGFR 45–59): Mild to moderately decreased function.
- Stage G3b (eGFR 30–44): Moderate to severely decreased function.
- Stage G4 (eGFR 15–29): Severely decreased function.
- Stage G5 (eGFR < 15): Kidney failure.
If your result is below 60 for three months or more, it may indicate chronic kidney disease. An eGFR below 15 suggests kidney failure, often requiring dialysis or a transplant. If you see an eGFR over 120, it is common for young, healthy individuals or those with high muscle mass, but it should be verified to ensure it is not a lab error.
Calculation logic verified using publicly available standards.
View our Accuracy & Reliability Framework →