Free GFR Calculator

The estimated glomerular filtration rate (eGFR) calculator—commonly known as the free GFR calculator—is a medical tool that helps detect kidney disease in its early stages. By using this kidney function calculator, you can estimate how effectively your kidneys are filtering waste from your blood. This guide explains the core concepts of eGFR, how to compute it using the CKD-EPI GFR formula or the MDRD GFR equation, and what the resulting numbers indicate about your kidney health.

What Is eGFR?

eGFR is a calculated measure of kidney filtration performance, expressed in mL/min/1.73 m². The factor 1.73 m² represents a standardized body surface area, which is why none of the validated equations include height or weight as variables. Creatinine levels can be affected by gender, race, muscle mass, physical activity, and certain medical conditions. Cystatin C, an alternative biomarker, is less influenced by muscle mass but can be altered by thyroid dysfunction or corticosteroid use. Therefore, the GFR blood test calculator allows you to compute eGFR based on either serum creatinine, serum cystatin C, or both.

Available Equations

According to the National Institute of Diabetes and Digestive and Kidney Diseases, four main equations are available for eGFR estimation. This eGFR calculator implements all four, enabling side‑by‑side comparison to see whether each yields values within the normal range. The tool is designed solely for adults aged 19 years or older; for pediatric patients, a dedicated pediatric eGFR calculator should be used.

CKD-EPI Creatinine Equation (2009)

This is the most recommended formula and requires only a serum creatinine measurement (SCr, in mg/dL):

$$\text{eGFR} = 141 \times \min\left(\frac{SCr}{k}, 1\right)^{\alpha} \times \max\left(\frac{SCr}{k}, 1\right)^{-1.209} \times 0.993^{\text{Age}} \times a \times b$$

where the coefficients depend on sex and race:

• For females: $\alpha = -0.329$, $k = 0.7$, $a = 1.018$; for males: $\alpha = -0.411$, $k = 0.9$, $a = 1$.
• Race factor $b$: 1.159 for Black patients, 1 for all others.

CKD-EPI Creatinine–Cystatin C Equation (2012)

This version adds serum cystatin C (Scys in mg/L) to improve accuracy for individuals with unusual diets or extreme muscle mass:

$$\text{eGFR} = 135 \times \min\left(\frac{SCr}{k}, 1\right)^{\alpha} \times \max\left(\frac{SCr}{k}, 1\right)^{-0.601} \times \min\left(\frac{Scys}{0.8}, 1\right)^{-0.375} \times \max\left(\frac{Scys}{0.8}, 1\right)^{-0.711} \times 0.995^{\text{Age}} \times a \times b$$

• Sex‑dependent parameters: For females $\alpha = -0.248$, $k = 0.7$, $a = 1.969$; for males $\alpha = -0.207$, $k = 0.9$, $a = 1$.
• Race factor $b$: 1.08 for Black patients, 1 for others.

CKD-EPI Cystatin C Equation (2012)

Useful when creatinine concentration is unstable (e.g., during pregnancy) or as a confirmatory test:

$$\text{eGFR} = 133 \times \min\left(\frac{Scys}{0.8}, 1\right)^{-0.499} \times \max\left(\frac{Scys}{0.8}, 1\right)^{-1.328} \times 0.996^{\text{Age}} \times a$$

• Coefficient $a$: 0.932 for females, 1 for males.
• This equation does not include a race term.

MDRD Study Equation

The Modification of Diet in Renal Disease (MDRD) formula is an alternative validated for adults aged 18–70 years with common causes of kidney disease:

$$\text{eGFR} = 175 \times SCr^{-1.154} \times \text{Age}^{-0.203} \times a \times b$$

• Factor $a$: 0.742 for females, 1 for males.
• Factor $b$: 1.212 for Black patients, 1 for others.

Interpreting eGFR Results

The table below, based on data from the National Kidney Foundation, summarizes typical eGFR ranges and corresponding kidney function stages:

eGFR (mL/min/1.73 m²)	Stage of Kidney Function
≥ 90	Normal or minimal damage
60–89	Mild loss of function
45–59	Mild to moderate loss
30–44	Moderate to severe loss
15–29	Severe loss
< 15	Kidney failure

Your individual results may vary depending on multiple factors. Always discuss your eGFR with a healthcare provider for a full assessment.

Managing Chronic Kidney Disease

Chronic kidney disease is most frequently caused by diabetes or hypertension, although immunological or inherited conditions can also be responsible. Detected early, CKD can often be slowed or halted. Advanced stages may require dialysis or a kidney transplant. If your eGFR values suggest decreased kidney function, seek medical advice for appropriate management.