GFR Calculator

GFR Calculator

The glomerular filtration rate (GFR) is an essential measure of kidney function. It estimates how much blood the kidneys filter each minute to remove waste products and excess fluids. Clinicians use estimated GFR to diagnose and monitor chronic kidney disease (CKD), to assess kidneys working over time, and to adjust medication doses to reduce the risk of side effects.

Estimated gfr also helps determine the likely stage of kidney disease a person has, which guides follow-up testing and dietary recommendations—particularly protein intake—since protein targets often change as kidney function declines.

Quick action:

Enter your serum creatinine, age, sex, and race into the gfr calculator on this page to get an estimated glomerular filtration rate and see the likely CKD stage. If your estimated gfr is low, share the result with your clinician for interpretation and next steps.

Table note: GFR ranges are shown as ml/min (original table values preserved). Clinical guidelines (KDIGO) typically report GFR normalized to ml/min/1.73 m² and subdivide Stage 3 into 3a (45–59) and 3b (30–44). Protein requirements are shown as in the source table; in clinical practice these are often expressed as g/kg/day—consult a dietitian or nephrologist for personalized diet guidance.

Calculation of GFR

Estimated glomerular filtration rate (GFR) is calculated using validated equations that combine a person’s serum creatinine, age, sex, and sometimes race. Serum creatinine — a waste product from muscle metabolism measured by a blood test — is central to these estimates because the kidneys normally filter creatinine from the blood; higher serum creatinine usually indicates lower kidney function.

The CKD-EPI equation (developed by the Chronic Kidney Disease Epidemiology Collaboration) is one commonly used formula; it generally estimates gfr more accurately than older equations across a wide range of kidney function. Clinical practice has evolved: older CKD-EPI versions included a race multiplier for Black patients, while newer refitted equations and institutional policies may prefer race‑free estimating equations — check local guidance when interpreting results.

When is measured GFR preferred? If precise kidney function is required (for example, before dosing certain chemotherapy agents or when transplant evaluation is underway), clinicians may order measured GFR tests (isotope or clearance studies). For routine monitoring and staging of ckd, estimated gfr from serum creatinine is the standard first step.

Example:

A 65‑year‑old woman with serum creatinine 1.0 mg/dL will have an estimated gfr calculated by the CKD‑EPI formula — use the gfr calculator above to enter your values and see a personalized estimate and likely CKD stage. If your estimated gfr is below 60 ml/min/1.73 m², discuss follow-up testing with your clinician.

Components of the CKD-EPI equation

To estimate glomerular filtration using CKD‑EPI, you need the person’s serum creatinine, sex, age, and race (if using the original race‑adjusted equation). Serum creatinine is measured by a blood test and is reported in mg/dL; it is a commonly used marker because the kidneys normally clear creatinine from the bloodstream.

The CKD‑EPI formula (one commonly used estimating equation) is shown below. The result is reported as estimated GFR in ml/min/1.73 m², which is the filtration rate normalized to a standard body surface area.

GFR (ml/min/1.73 m²) = 141 x min(Serum creatinine/κ, 1)^α x max(Serum creatinine/κ, 1)^-1.209 x 0.993^Age x 1.018 [if female] x 1.159 [if Black]

Where:

Serum creatinine — creatinine level in the blood measured in mg/dL by a blood test.

κ (kappa) — constant that depends on sex (0.7 for females, 0.9 for males).

α (alpha) — exponent that varies by sex and age category (values used in clinical calculators; confirm exact α for your calculator implementation).

Note: The numeric constants shown (141, -1.209 exponent, 0.993 per year) reflect the original CKD‑EPI formulation. Many clinical teams now reference race‑free estimating equations or institutional policies when reporting estimated gfr — check local guidance (and the original CKD‑EPI sources such as the Ann Intern Med publications or subsequent refits like the 2021 van Lente/CKD‑EPI updates) when implementing the formula.

Worked example (illustrative):

If a 60‑year‑old man has serum creatinine 1.2 mg/dL, a calculator using the CKD‑EPI formula will apply κ=0.9 and the relevant α to compute an estimated gfr (use the gfr calculator on this page for exact numeric output). Remember, estimated gfr is a screening and monitoring tool; when precise kidney function measurement is required (e.g., certain medication dosing or transplant workup), measured GFR tests may be ordered.

Caveats: keep the units consistent (serum creatinine in mg/dL, age in years), and be aware that factors such as extremes of body size, muscle mass, or rapidly changing kidney function can affect the accuracy of estimating equations. If your calculated gfr is <60 ml/min/1.73 m² or shows progressive decline across stages, follow up with your clinician for further assessment.

Disclaimer: The values generated by this gfr calculator are approximate estimates only and are intended for informational purposes. They do not replace a medical diagnosis or personalized advice from a qualified healthcare professional. Estimated gfr can be affected by factors such as age, body size, muscle mass, weight, and ethnicity, and may be less accurate in people with rapidly changing kidney function, extremes of body composition, or acute illness.

What to do next:

1. If your estimated gfr is <60 ml/min/1.73 m² or you have symptoms of kidney problems (swelling, decreased urine output, unexplained fatigue), contact your clinician for follow-up testing to determine the stage of kidney disease and next steps.
2. Bring your recent blood test results (serum creatinine and other labs) to your primary care provider or nephrologist to discuss kidney function, medication adjustments, and whether a referral is needed for chronic kidney disease or renal disease management.
3. If dietary guidance is needed, ask your clinician for a referral to a registered dietitian experienced in CKD nutrition to discuss appropriate protein and diet plans that help slow progression and protect kidney health.
4. For people with high blood pressure or uncontrolled diabetes — common causes of kidney damage — work with your care team to optimize blood pressure and blood sugar control to reduce the risk of kidney failure.

If you are preparing for a kidney transplant evaluation or need precise kidney function for medication dosing, clinicians may order measured GFR tests or specialist assessment. For general monitoring of kidney function and stages of chronic kidney disease, estimated gfr from a blood test is the usual first step. Always consult your healthcare team to interpret results and plan care.