Free GFR calculator estimates your kidney function using the race-free CKD-EPI 2021 or MDRD equations. Includes CKD staging, interpretation, and step-by-step math.
This calculator provides estimates for educational purposes only. eGFR equations have limitations and may not be accurate in all clinical scenarios including muscle wasting, malnutrition, amputees, pregnancy, or acute kidney injury. Always consult a healthcare provider for medical decisions.
CKD-EPI 2021 is the recommended equation for GFR estimation. This race-free version is endorsed by the NKF and ASN (2021).
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Glomerular filtration rate (GFR) is the gold standard for measuring kidney function. Our calculator uses the CKD-EPI 2021 equation — the current recommended formula endorsed by the National Kidney Foundation and American Society of Nephrology — to estimate your eGFR from serum creatinine, age, and sex. Get instant results with CKD stage classification, age-adjusted context, and step-by-step calculation breakdown.
GFR (glomerular filtration rate) measures how much blood your kidneys filter per minute. It's the best overall indicator of kidney function and is used to diagnose and stage chronic kidney disease (CKD). Since directly measuring GFR requires complex procedures, healthcare providers use estimated GFR (eGFR) equations that calculate GFR from blood tests. The CKD-EPI 2021 equation is the current standard, using only serum creatinine, age, and sex — without race — to provide accurate estimates across diverse populations.
CKD-EPI 2021 Equation
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(-1.200) × 0.9938^Age × 1.012 [if female]Uses the CKD-EPI 2021 equation recommended by the National Kidney Foundation and American Society of Nephrology for accurate eGFR estimation.
The 2021 update removed race as a variable, providing equitable and accurate results for all patients regardless of race or ethnicity.
Automatically classifies your result into CKD stages G1-G5 with color-coded results and clinical descriptions.
Compares your eGFR to expected values for your age group, since GFR naturally declines with age.
Choose between CKD-EPI 2021 (recommended) or MDRD (legacy) equations based on your clinical needs.
Enter creatinine in mg/dL or µmol/L — the calculator handles conversion automatically.
View the complete calculation breakdown with professional mathematical notation for education and verification.
Nephrologists use eGFR to diagnose chronic kidney disease and classify patients into stages G1-G5, guiding treatment decisions and monitoring disease progression.
Primary care providers screen patients with diabetes, hypertension, or family history of kidney disease using eGFR to detect kidney problems early.
Many drugs require dose adjustments based on kidney function. Pharmacists and physicians use eGFR to ensure safe dosing of medications like metformin, anticoagulants, and contrast agents.
Transplant teams assess eGFR to evaluate kidney function in potential donors and recipients during the organ transplantation process.
Patients with CKD or those at risk can monitor their kidney function over time by calculating eGFR from routine lab work and comparing trends.
Medical students and healthcare trainees learning nephrology can practice GFR calculations and understand how patient factors affect kidney function estimates.
A normal GFR is above 90 mL/min/1.73m² (CKD Stage 1). However, GFR naturally declines with age — a 70-year-old with an eGFR of 75 may have normal age-related kidney function, while the same value in a 30-year-old could indicate kidney disease. An eGFR of 60-89 indicates mildly decreased function (Stage 2), and values below 60 suggest chronic kidney disease requiring medical attention.
GFR (glomerular filtration rate) is the actual rate at which your kidneys filter blood, measured by specialized tests. eGFR (estimated GFR) is calculated from blood creatinine, age, and sex using equations like CKD-EPI 2021. Since direct GFR measurement is complex and expensive, eGFR is used in routine clinical practice and provides accurate estimates for most patients.
The CKD-EPI 2021 equation removed race because the original race-based adjustments were based on flawed assumptions about muscle mass differences and led to health disparities. Studies showed that using race could delay CKD diagnosis and treatment access for Black patients. The new equation performs well across all racial and ethnic groups without needing race as a variable.
CKD-EPI 2021 is the current recommended equation for estimating GFR. Developed by the Chronic Kidney Disease Epidemiology Collaboration and endorsed by the NKF and ASN, it uses serum creatinine, age, and sex (without race) to calculate eGFR. It's more accurate than older equations, especially for eGFR values above 60 mL/min/1.73m².
CKD-EPI 2021 is the newer, recommended equation that performs better at higher GFR values (≥60) and doesn't use race. MDRD (Modification of Diet in Renal Disease) is an older equation from 1999 that tends to underestimate GFR in healthy people. CKD-EPI is preferred for CKD screening and staging, while MDRD may still be reported by some laboratories.
CKD is classified into 5 stages based on eGFR: Stage G1 (≥90, normal), Stage G2 (60-89, mildly decreased), Stage G3a (45-59, mild-moderate decrease), Stage G3b (30-44, moderate-severe decrease), Stage G4 (15-29, severely decreased), and Stage G5 (<15, kidney failure). Treatment intensity increases with advancing stages.
GFR naturally declines by about 1 mL/min/year after age 40 due to loss of functional nephrons (kidney filtering units), reduced blood flow, and structural changes in kidney tissue. An 80-year-old may have an eGFR of 65 as a normal part of aging, while the same value in a 40-year-old would indicate kidney disease.
To convert serum creatinine from µmol/L to mg/dL, divide by 88.4. For example, 100 µmol/L ÷ 88.4 = 1.13 mg/dL. US laboratories typically report in mg/dL, while international labs often use µmol/L. Our calculator handles this conversion automatically.
eGFR equations may be inaccurate in patients with unusual muscle mass (bodybuilders, amputees, muscle wasting), acute kidney injury, pregnancy, certain diets (high protein, creatine supplements), or taking medications that affect creatinine secretion. In these cases, direct GFR measurement with iohexol or 24-hour creatinine clearance may be needed.
Cystatin C is an alternative biomarker for estimating GFR. Unlike creatinine, cystatin C is not affected by muscle mass, making it more accurate in certain patients. Some laboratories report eGFR using cystatin C alone or combined with creatinine for improved accuracy, especially in patients where creatinine-based estimates may be unreliable.
eGFR (using CKD-EPI) is preferred for CKD diagnosis, staging, and monitoring. Creatinine clearance (using Cockcroft-Gault) is still commonly used for medication dose adjustments because many drug studies and FDA labeling reference CrCl. For drug dosing, check the specific medication's prescribing information to see which measure is recommended.