GFR Calculator (eGFR CKD-EPI 2021)
Estimate glomerular filtration rate (eGFR) using the CKD-EPI 2021 creatinine equation, classify CKD stage, and interpret kidney function.
For educational support only. Does not replace clinical judgment or local laboratory reference ranges.
GFR Calculator
What is GFR (glomerular filtration rate)?
Glomerular filtration rate (GFR) is the best overall index of kidney function. It estimates how much blood your kidneys filter each minute, usually expressed as mL/min/1.73 m². Because direct measurement is complex, laboratories report an estimated GFR (eGFR) calculated from serum creatinine, age, and sex.
Formulas used in this GFR calculator
1. CKD-EPI 2021 creatinine equation (race-free)
This calculator uses the 2021 CKD-EPI equation, which removes race from the formula and is recommended by major guidelines.
General form:
For serum creatinine in mg/dL: \[ \text{eGFR} = 142 \times \min\left(\frac{\text{Scr}}{\kappa}, 1\right)^{\alpha} \times \max\left(\frac{\text{Scr}}{\kappa}, 1\right)^{-1.200} \times 0.9938^{\text{Age}} \times S \]
- Scr = serum creatinine (mg/dL)
- For females: κ = 0.7, α = −0.241, S = 1.012
- For males: κ = 0.9, α = −0.302, S = 1.000
- Age in years
2. Legacy CKD-EPI 2009 equation (with race coefficient)
For comparison, you can optionally display the older CKD-EPI 2009 equation, which included a race coefficient for Black vs non-Black patients. Many centers are transitioning away from this approach.
General form (mg/dL):
\[ \text{eGFR} = 141 \times \min\left(\frac{\text{Scr}}{\kappa}, 1\right)^{\alpha} \times \max\left(\frac{\text{Scr}}{\kappa}, 1\right)^{-1.209} \times 0.993^{\text{Age}} \times S_{\text{sex}} \times S_{\text{race}} \]
- For females: κ = 0.7, α = −0.329, Ssex = 1.018
- For males: κ = 0.9, α = −0.411, Ssex = 1.000
- For Black race: Srace = 1.159; otherwise 1.000
3. Creatinine unit conversion
\[ \text{Scr (mg/dL)} = \frac{\text{Scr (µmol/L)}}{88.4} \]
4. Body surface area (BSA) and absolute GFR
Standard eGFR is normalized to a body surface area of 1.73 m². To estimate absolute GFR in mL/min, this calculator uses the Du Bois formula for BSA:
\[ \text{BSA} = 0.007184 \times \text{Height}^{0.725} \times \text{Weight}^{0.425} \] (Height in cm, Weight in kg)
\[ \text{Absolute GFR (mL/min)} = \text{eGFR (mL/min/1.73 m²)} \times \frac{\text{BSA}}{1.73} \]
CKD stages by eGFR
The calculator classifies kidney function according to KDIGO categories:
| Stage | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high (CKD only if other kidney damage markers are present) |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure (end-stage kidney disease) |
How to interpret your eGFR result
- eGFR ≥ 90: Usually normal. CKD is diagnosed only if there are other signs of kidney damage (e.g. albuminuria, structural abnormalities).
- eGFR 60–89: Mild reduction. Often normal in older adults; interpret with urine tests and clinical context.
- eGFR 45–59 (G3a): Mild–moderate CKD. Consider nephrology referral if persistent or if other risk factors are present.
- eGFR 30–44 (G3b): Moderate–severe CKD. Higher risk of complications; specialist follow-up is usually recommended.
- eGFR 15–29 (G4): Severe CKD. Preparation for possible kidney replacement therapy (dialysis or transplant).
- eGFR < 15 (G5): Kidney failure. Urgent specialist management is required.
When is eGFR less reliable?
Creatinine-based eGFR can be inaccurate in situations where muscle mass or creatinine production is very different from average, for example:
- Pregnancy
- Very muscular or very low muscle mass (bodybuilders, frail elderly, amputees)
- Severe liver disease
- Rapidly changing kidney function (acute kidney injury)
- Extremes of diet (very high or very low protein intake)
In these cases, clinicians may use cystatin C–based equations or direct GFR measurement.
Frequently asked questions
Is an eGFR of 60 normal?
An eGFR around 60 mL/min/1.73 m² is at the lower limit of normal. In older adults it may be acceptable, but if it is persistent or accompanied by albumin in the urine, it may indicate early chronic kidney disease.
How often should GFR be checked?
People with diabetes, hypertension, cardiovascular disease, or known kidney disease are usually monitored at least once a year, sometimes more frequently depending on risk and previous results. Follow your clinician’s recommendations.
Can I improve my eGFR?
Some causes of reduced eGFR are reversible (e.g. dehydration, obstruction, certain medications). Chronic kidney disease is often progressive, but good blood pressure and blood sugar control, avoiding nephrotoxic drugs, and healthy lifestyle choices can slow progression. Always discuss treatment options with your healthcare provider.
Medical disclaimer
This tool is for informational and educational purposes only. It does not provide medical advice, diagnosis, or treatment and must not be used as a substitute for professional medical judgment. Always consult your doctor or nephrologist for decisions about your health and laboratory results.