GFR Calculator - Free Online Tool

Estimate your glomerular filtration rate with CKD-EPI 2021, MDRD, and Cockcroft-Gault formulas

Welcome to our free eGFR (estimated Glomerular Filtration Rate) Calculator, the most comprehensive kidney function tool available online. This calculator uses multiple validated clinical formulas — including the current gold-standard CKD-EPI 2021 equation — to estimate how well your kidneys are filtering waste from your blood. Knowing your eGFR is essential for understanding kidney health, diagnosing and monitoring chronic kidney disease (CKD), and making informed decisions about medications and lifestyle changes. Glomerular filtration rate measures the volume of fluid filtered by the kidney's glomeruli per minute, normalized to a standard body surface area of 1.73 m². In healthy adults, the GFR typically ranges from 90 to 120 mL/min/1.73 m², though it naturally declines with age. Because GFR cannot be measured directly in a clinical setting without complex procedures, clinicians use serum creatinine levels — a waste product of muscle metabolism — along with age, sex, and other variables to estimate GFR through validated equations. Our calculator implements four major equations simultaneously. The CKD-EPI Creatinine 2021 equation is the current primary recommendation from the National Kidney Foundation (NKF) and American Society of Nephrology (ASN). Adopted in September 2021, this race-free formula removed the race coefficient that appeared in the older 2009 version, addressing long-standing equity concerns in medical practice. The removal of the race variable ensures that patients are not assigned a higher eGFR value — and thus delayed referral to nephrology — simply due to their racial background. If you have previously had an eGFR calculated using an older equation, your value under CKD-EPI 2021 may differ slightly. The MDRD (Modification of Diet in Renal Disease) Study Equation has been widely used since 1999 and remains the reference equation in many laboratory systems. Our calculator uses the 2006 IDMS-standardized revision with the constant 175. The MDRD equation tends to underestimate GFR when kidney function is normal (above 60 mL/min/1.73 m²), which is why CKD-EPI 2021 is now preferred for general use. MDRD is most accurate for eGFR values below 60. The Cockcroft-Gault formula estimates creatinine clearance (CrCl) rather than true eGFR. It was developed in 1976 and requires body weight as an additional input. The result is expressed in mL/min without normalization to body surface area, which makes it particularly useful for calculating medication doses — most drug prescribing information references Cockcroft-Gault CrCl thresholds. Important medications that require dose adjustment based on kidney function include metformin (contraindicated below CrCl 30 mL/min), direct oral anticoagulants like rivaroxaban and apixaban, certain antibiotics, and several chemotherapy agents. Chronic kidney disease is classified into five stages based on eGFR, following the KDIGO (Kidney Disease: Improving Global Outcomes) guidelines. Stage G1 (eGFR ≥90) represents normal or high kidney function, though CKD may still be present if markers of kidney damage such as proteinuria are detected. Stage G2 (60-89) indicates mildly decreased function. Stage G3 is subdivided into G3a (45-59, mildly to moderately decreased) and G3b (30-44, moderately to severely decreased). Stage G4 (15-29) represents severely decreased function and typically requires preparation for kidney replacement therapy. Stage G5 (below 15) is kidney failure, also called end-stage renal disease (ESRD), where dialysis or transplantation is necessary. Importantly, a diagnosis of CKD requires the same eGFR abnormality or kidney damage marker to persist for at least three months. A single low eGFR reading does not confirm CKD — it could reflect acute kidney injury (AKI), dehydration, recent strenuous exercise, or a medication effect. Always repeat testing and consult a healthcare provider before drawing any conclusions from a single result. This calculator also provides the KDIGO risk stratification when you enter your albumin-to-creatinine ratio (ACR). Combining the eGFR category with the ACR category produces a risk matrix ranging from Low to Very High, which guides monitoring frequency and referral decisions. Patients with G3b-G4 or high ACR categories are typically referred to nephrology, while G1-G2 with low ACR may be managed in primary care. All calculations in this tool run entirely within your browser. No health data is transmitted to any server. The unit toggle converts serum creatinine between mg/dL (used in the US) and µmol/L (used internationally). Height and weight inputs unlock the Cockcroft-Gault CrCl and BSA-adjusted absolute GFR. The results are displayed side by side for easy formula comparison, along with a visual kidney function gauge showing your position across the G1-to-G5 spectrum. This tool is intended for informational and educational purposes. Always discuss your eGFR results with a qualified healthcare professional.

Understanding GFR and Kidney Function

Glomerular filtration rate (GFR) is the standard measure of kidney function. It reflects how efficiently your kidneys filter waste products and excess fluid from the blood each minute.

What Is GFR and Why Does It Matter?

GFR stands for Glomerular Filtration Rate — the volume of blood plasma filtered by the kidneys each minute, expressed in mL/min/1.73 m² (normalized to average adult body surface area). It is the best overall measure of kidney function and is used to detect, stage, and monitor chronic kidney disease. A healthy adult typically has a GFR between 90 and 120. GFR naturally declines with age at roughly 1 mL/min per year after age 40. Because measuring true GFR requires infusing a marker substance like inulin or iohexol, clinicians estimate it (eGFR) from a simple blood creatinine test plus demographic variables. Your eGFR is reported by most standard blood panels and is a routine part of metabolic screening.

CKD Staging: G1 Through G5

KDIGO (Kidney Disease: Improving Global Outcomes) classifies chronic kidney disease into five GFR categories. G1 (eGFR ≥90 mL/min/1.73 m²): Normal or high kidney function. CKD can still exist at G1 if kidney damage markers such as proteinuria or structural abnormalities are present. G2 (60-89): Mildly decreased function, often with no symptoms. G3a (45-59): Mildly to moderately decreased — the stage where complications like anemia and bone disease begin to emerge. G3b (30-44): Moderately to severely decreased — higher risk for cardiovascular events and CKD progression. G4 (15-29): Severely decreased — preparation for kidney replacement therapy (dialysis or transplant) should begin. G5 (below 15): Kidney failure — also called end-stage renal disease (ESRD). CKD diagnosis requires these findings to persist for three or more months.

The CKD-EPI 2021 Formula Explained

The CKD-EPI Creatinine 2021 equation is the current gold-standard formula for estimating GFR in adults. It was developed by the CKD-EPI Collaboration and endorsed by the NKF-ASN Task Force in 2021. The key improvement over the 2009 version is the removal of the race coefficient. Previous research had found that Black patients had, on average, higher serum creatinine levels, leading to higher eGFR values when a race multiplier was applied. This resulted in delayed CKD diagnosis and referral for Black patients. The 2021 equation eliminates this variable entirely, applying the same calculation regardless of self-reported race. The formula uses serum creatinine, age, and sex-specific constants to produce an estimate in mL/min/1.73 m².

When Should You Get Your GFR Tested?

Your doctor may order a serum creatinine test (from which eGFR is calculated) as part of a routine metabolic panel, or specifically if you have risk factors for kidney disease. High-risk groups who should have regular eGFR monitoring include people with type 1 or type 2 diabetes, hypertension (high blood pressure), family history of kidney disease, recurrent kidney stones, frequent use of NSAIDs (ibuprofen, naproxen) or other nephrotoxic medications, obesity, cardiovascular disease, and people over age 60. The monitoring frequency depends on your CKD stage and ACR category — G1-G2 with low ACR may only need annual testing, while G4-G5 may need testing every 1-3 months. If you are tracking your eGFR over time, use this calculator to log each result and note the trend.

Formulas

CKD-EPI Creatinine 2021 (Race-Free)

eGFR = 142 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^(−1.200) × 0.9938^Age × (1.012 if female)

The current gold-standard equation recommended by NKF and ASN since 2021. κ = 0.7 (female) or 0.9 (male); α = −0.241 (female) or −0.302 (male). Uses serum creatinine (SCr), age, and sex only — no race coefficient.

MDRD Study Equation (IDMS-Standardized)

eGFR = 175 × SCr^(−1.154) × Age^(−0.203) × (0.742 if female) × (1.212 if Black)

The Modification of Diet in Renal Disease equation, revised in 2006 for IDMS-standardized creatinine. Most accurate for eGFR below 60 mL/min/1.73 m². Tends to underestimate when kidney function is normal.

Cockcroft-Gault Creatinine Clearance

CrCl = ((140 − Age) × Weight in kg × (0.85 if female)) / (72 × SCr in mg/dL)

Estimates creatinine clearance (mL/min) rather than true eGFR. Not normalized to body surface area. Used primarily for medication dose calculations, as most drug prescribing references Cockcroft-Gault thresholds.

Schwartz Bedside (Pediatric)

eGFR = 0.413 × Height (cm) / SCr (mg/dL)

The simplified Schwartz formula for estimating GFR in children aged 1-17. Uses height and serum creatinine only. Validated for use with IDMS-traceable creatinine assays.

Reference Tables

CKD Stages by GFR

Chronic kidney disease stages as defined by KDIGO guidelines, based on estimated glomerular filtration rate.

Stage	eGFR (mL/min/1.73 m²)	Classification	Clinical Significance
G1	≥ 90	Normal or high	CKD may exist if damage markers present; annual monitoring if at risk
G2	60 – 89	Mildly decreased	Often no symptoms; CKD diagnosed only with persistent damage markers
G3a	45 – 59	Mildly to moderately decreased	Anemia and bone disease may begin; BP control important
G3b	30 – 44	Moderately to severely decreased	Elevated cardiovascular risk; nephrology referral considered
G4	15 – 29	Severely decreased	Preparation for dialysis or transplant; symptoms may appear
G5	< 15	Kidney failure (ESRD)	Dialysis or transplantation required to sustain life

Albuminuria Categories (ACR)

KDIGO albuminuria categories used alongside GFR staging for risk stratification.

Category	ACR (mg/g)	Classification	Monitoring Frequency
A1	< 30	Normal to mildly increased	Annual if at risk
A2	30 – 300	Moderately increased (microalbuminuria)	Every 6 months
A3	> 300	Severely increased (macroalbuminuria)	Every 3 months or more frequently

Worked Examples

CKD-EPI 2021 for 55-Year-Old Male with Creatinine 1.2 mg/dL

A 55-year-old male has a serum creatinine of 1.2 mg/dL. Calculate eGFR using CKD-EPI 2021.

For males: κ = 0.9, α = −0.302

SCr/κ = 1.2 / 0.9 = 1.333 (greater than 1, so use max term)

min(1.333, 1)^(−0.302) = 1^(−0.302) = 1.0

max(1.333, 1)^(−1.200) = 1.333^(−1.200) = 0.727

Age factor: 0.9938^55 = 0.710

Sex factor: 1.0 (male)

eGFR = 142 × 1.0 × 0.727 × 0.710 × 1.0 = 73.3 mL/min/1.73 m²

eGFR is approximately 73 mL/min/1.73 m², classified as CKD Stage G2 (mildly decreased). This is within the expected range for a 55-year-old but warrants monitoring if risk factors are present.

Cockcroft-Gault for 72-Year-Old Female

A 72-year-old female weighing 60 kg has a serum creatinine of 1.4 mg/dL. Calculate creatinine clearance for medication dosing.

CrCl = ((140 − Age) × Weight × 0.85) / (72 × SCr)

CrCl = ((140 − 72) × 60 × 0.85) / (72 × 1.4)

CrCl = (68 × 60 × 0.85) / 100.8

CrCl = 3,468 / 100.8 = 34.4 mL/min

Creatinine clearance is approximately 34 mL/min. This corresponds roughly to CKD Stage G3b. Medications like metformin may require dose reduction, and certain drugs may be contraindicated below 30 mL/min.

How to Use the GFR Calculator

Enter Your Serum Creatinine

Find your serum creatinine value on a blood test report (a standard metabolic panel or kidney function panel includes this). Toggle between mg/dL (used in the US) and µmol/L (used in most other countries) to match your lab report. Typical adult values range from 0.5 to 1.2 mg/dL (44 to 106 µmol/L). Higher values generally indicate reduced kidney function.

Enter Age and Biological Sex

Type your age in years and select your biological sex (Male or Female). These are required for all GFR equations. The sex selection affects the sex-specific constants (kappa and alpha) in the CKD-EPI formulas. Age directly appears in the exponent of both CKD-EPI and MDRD equations — GFR naturally declines with age, so the formulas account for this.

Add Optional Inputs for More Results

Expand the Advanced Options section to enter additional values. Weight (kg or lbs) enables the Cockcroft-Gault creatinine clearance calculation — useful for checking medication dose thresholds. Height (cm or inches) combined with weight enables BSA-adjusted absolute GFR. Serum Cystatin C (mg/L) unlocks two additional equations. ACR (albumin-to-creatinine ratio) category enables the KDIGO risk matrix, which shows your combined kidney disease and cardiovascular risk.

Review the Side-by-Side Formula Comparison

Click Calculate eGFR to see all results simultaneously. The primary CKD-EPI 2021 result appears prominently with your CKD stage. The formula comparison table shows CKD-EPI 2021, CKD-EPI 2009, MDRD, and Cockcroft-Gault side by side — making it easy to compare how different equations interpret the same values. The kidney function spectrum gauge shows your position within the G1-to-G5 range visually.

Frequently Asked Questions

What is a normal eGFR, and does it change with age?

A normal eGFR is typically 90 mL/min/1.73 m² or above for adults. GFR naturally declines with age at approximately 1 mL/min per year after age 40, which is why an eGFR of 75 in a 70-year-old may not indicate disease, while the same value in a 30-year-old would be concerning. The population reference chart in this calculator shows typical eGFR values by decade: roughly 116 for ages 20-29, dropping to 85 for ages 60-69, and 75 for ages 70 and over. Whether a given eGFR represents CKD depends on whether kidney damage markers (like protein in urine) co-exist and whether the finding persists for at least three months. Always review your result in the context of your age and medical history with your doctor.

Why does the CKD-EPI 2021 formula no longer use race?

The original CKD-EPI 2009 equation included a multiplier of 1.159 for patients identified as Black, based on population studies showing higher average muscle mass and creatinine production in Black individuals. However, this approach was criticized for assigning a biological characteristic to a socially defined category, and its application led to Black patients being assigned systematically higher eGFR values — and consequently later referrals to nephrology. An NKF-ASN Task Force reviewed the evidence in 2021 and concluded that race should not be a variable in kidney function equations. The new 2021 CKD-EPI formula uses only creatinine, age, and sex. The change may lower the eGFR for some patients who were previously using the Black race coefficient, which could lead to earlier identification and treatment of CKD.

What is the difference between eGFR and creatinine clearance (Cockcroft-Gault)?

eGFR from CKD-EPI or MDRD is expressed in mL/min/1.73 m² — it is normalized to a standard body surface area of 1.73 m², making it comparable across patients of different body sizes. Creatinine clearance (CrCl) from the Cockcroft-Gault formula is expressed in mL/min without body surface area normalization. CrCl tends to slightly overestimate true GFR because creatinine is not only filtered but also secreted by renal tubules. Despite this, Cockcroft-Gault remains the standard reference in drug prescribing information because it was the equation used in most pharmacokinetic studies. When checking medication dose thresholds — for example, whether to use metformin or how to dose a direct oral anticoagulant — always use Cockcroft-Gault CrCl, not eGFR.

When is the MDRD equation used instead of CKD-EPI?

The MDRD (Modification of Diet in Renal Disease) Study Equation was the standard eGFR formula from 1999 until CKD-EPI was introduced in 2009. MDRD is less accurate than CKD-EPI when eGFR is above 60 mL/min/1.73 m² — it tends to underestimate eGFR in this range, which can lead to overdiagnosis of CKD. CKD-EPI 2021 is now recommended for all adults in clinical practice. However, MDRD may still appear in some older laboratory systems that have not yet updated their reporting, and it remains useful for reference and comparison purposes. This calculator shows MDRD alongside CKD-EPI so you can see how the two equations differ for your specific inputs.

What does the KDIGO risk matrix mean, and when is referral to a nephrologist needed?

KDIGO (Kidney Disease: Improving Global Outcomes) risk stratification combines your GFR category (G1-G5) with your albuminuria category (A1, A2, or A3 based on urine albumin-to-creatinine ratio). Together, these two dimensions create a heat map of risk from Low to Very High. Low risk means annual monitoring in primary care is sufficient. Moderately Increased risk generally means monitoring every 6 months. High risk warrants every 3-month checks. Very High risk requires monthly to 3-monthly monitoring and specialist nephrology care. Referral to a nephrologist is typically recommended when eGFR is below 30 mL/min/1.73 m² (G4-G5), when eGFR is declining rapidly (more than 5 mL/min/1.73 m² per year), when ACR is in the severely increased category (A3), or when the cause of kidney disease is uncertain.

Can medications or other factors falsely alter my creatinine and eGFR?

Yes, several factors can affect serum creatinine independent of actual kidney function, which leads to either falsely high or falsely low eGFR. Medications that reduce creatinine secretion without harming the kidney include trimethoprim, cimetidine, and certain diabetes drugs — these raise creatinine and lower apparent eGFR. High dietary meat intake can transiently raise creatinine. Strenuous exercise increases creatinine for 24-48 hours. Conversely, very low muscle mass (elderly, amputees, malnutrition) produces less creatinine, artificially lowering it and inflating eGFR. Dehydration concentrates creatinine, lowering apparent eGFR. Pregnancy lowers creatinine and inflates eGFR. For these reasons, eGFR from creatinine alone is considered less reliable in these special populations, and Cystatin C-based or combined equations may be more accurate.