Glomerular Filtration Rate (GFR) Calculator

About the Glomerular Filtration Rate (GFR) Calculator

The Glomerular Filtration Rate (GFR) Calculator estimates kidney filtration with four commonly used equations: CKD-EPI, MDRD, Cockcroft-Gault, and CKD-EPI cystatin C. eGFR is widely used for CKD staging and medication review, but it remains an estimate rather than a direct measurement of filtration.

The CKD-EPI creatinine equation revision used on this page removed the race coefficient used in earlier versions after National Kidney Foundation (NKF) and American Society of Nephrology (ASN) Task Force recommendations. It is widely used for adult creatinine-based eGFR reporting.

This calculator can organize CKD stage, albuminuria category, and equation comparison in one place. Medication dosing, referral decisions, and CKD diagnosis should still be confirmed against guideline review, repeat testing, and the clinical context.

When This Page Helps

Equation choice can matter near staging and dosing thresholds, and side-by-side comparison can make those differences easier to see. The calculator is best used as a structured reference and discussion aid rather than a substitute for lab reporting, repeat measurements, or clinician judgment.

How to Use the Inputs

1. Enter serum creatinine value and select the unit (mg/dL or µmol/L).
2. Enter age and select sex for CKD-EPI and MDRD calculation.
3. For Cockcroft-Gault, also enter body weight (and height for BSA-adjusted value).
4. Optionally enter cystatin C, urine albumin-to-creatinine ratio, and BUN for additional analysis.
5. Review CKD stage, risk category, drug dosing alerts, and equation comparison.

Example Calculation

Tips & Best Practices

• The CKD-EPI race-free equation is widely used for adult creatinine-based eGFR. MDRD is less accurate, especially when GFR >60.
• Cockcroft-Gault is still required by some FDA drug labels — it estimates creatinine clearance (CrCl), not GFR, and is not BSA-indexed.
• Creatinine is affected by muscle mass, meat intake, creatine supplements, and certain drugs (trimethoprim, cimetidine block tubular secretion and raise creatinine without changing GFR).
• Confirm CKD with two eGFR measurements at least 90 days apart — a single low eGFR may reflect acute kidney injury, not CKD.
• Cystatin C is useful when creatinine is unreliable: very muscular patients (creatinine overestimates GFR), amputees, or those with very low muscle mass (creatinine underestimates GFR).
• An eGFR drop of >5 mL/min/year or >25% decline from baseline can suggest rapid progression and may prompt closer follow-up or nephrology review.

CKD-EPI vs. Earlier Equations

The CKD-EPI race-free equation revision used on this page was developed from a pooled dataset of 12 studies (N = 15,049) without using race as a variable. Compared with CKD-EPI 2009 without the race coefficient, the revised equation shows less bias and similar precision. For Black individuals, it generally produces slightly lower eGFR estimates than the 2009 equation with the race coefficient, which may lead to earlier CKD detection and referral. For non-Black individuals, results are very similar to CKD-EPI 2009. The MDRD equation, while historically important, systematically underestimates GFR above 60 mL/min and is no longer the preferred reporting equation in many settings.

Measured GFR

The gold standard for GFR measurement is clearance of an exogenous filtration marker: iohexol, iothalamate, inulin, or ⁵¹Cr-EDTA. Measured GFR (mGFR) involves IV injection of the marker and timed blood or urine sampling. It is expensive and time-consuming, so it is reserved for situations requiring high accuracy: kidney donor evaluation, clinical trials, monitoring nephrotoxic chemotherapy, confirming CKD in borderline cases, and patients where eGFR is unreliable.

Albuminuria and Cardiovascular Risk

Albuminuria is an independent kidney and cardiovascular risk marker, not just a CKD staging detail. The KDIGO risk matrix combines GFR and albuminuria categories to guide monitoring intensity and referral discussions. Medication choices such as renin-angiotensin system blockers or SGLT2 inhibitors depend on the broader diagnosis, lab pattern, and clinician review rather than eGFR alone.

Frequently Asked Questions

• Why was the race coefficient removed from GFR equations?

  The CKD-EPI 2009 and MDRD equations included a race coefficient (multiplied eGFR by 1.159 for Black patients) based on the observation that Black individuals in the study cohort had higher average creatinine at the same measured GFR. However, this coefficient conflated race with biological characteristics, delayed CKD diagnosis in some Black patients, delayed referral and transplant listing, and perpetuated racial bias in clinical practice. NKF-ASN Task Force guidance recommended race-free equations, and the CKD-EPI revision removed race as a variable.

• Which GFR equation should I use?

  The CKD-EPI creatinine equation used on this page is widely used for adults. Use Cockcroft-Gault only when a specific drug label requires it. Use CKD-EPI cystatin C when creatinine is unreliable, such as with extremes of muscle mass, vegetarian diet, a recent meat meal, or creatine supplements. For children, none of these equations apply — use pediatric equations instead.

• What is the difference between GFR and creatinine clearance?

  GFR measures the volume of plasma filtered by the glomeruli per minute (the "true" measure of kidney function). Creatinine clearance (CrCl) measures the volume of plasma cleared of creatinine per minute. They differ because creatinine is not only filtered but also secreted by the proximal tubule, making CrCl ~10–15% higher than GFR. This difference increases as GFR declines (proportionally more tubular secretion). CKD-EPI and MDRD estimate GFR; Cockcroft-Gault estimates CrCl. For clinical purposes, they are often used interchangeably, but for drug dosing, use whichever the drug label specifies.

• Can eGFR be inaccurate?

  Yes. eGFR equations are population-level estimations with imprecision of ±30% (a reported eGFR of 60 could be truly 42–78). Common causes of inaccuracy: 1) Extreme muscle mass (bodybuilders: creatinine high, eGFR falsely low), 2) Malnutrition/amputees (low creatinine, eGFR falsely high), 3) Acute kidney injury (creatinine is rising and hasn't equilibrated — eGFR overestimates function), 4) Vegetarian diet (lower creatinine from lower creatine intake), 5) Drugs that inhibit creatinine secretion (trimethoprim, cimetidine — raise creatinine without changing GFR), 6) Pregnancy (GFR increases physiologically; equations may not apply). When precise GFR is needed, consider measured GFR (iohexol or iothalamate clearance).

• What is eGFR >60 with albuminuria?

  eGFR ≥60 does not rule out CKD. CKD is defined as kidney damage or GFR <60 for at least 3 months. Albuminuria (ACR ≥30 mg/g) can represent kidney damage even with normal eGFR. A patient with eGFR 95 and ACR 200 mg/g may still fall into a CKD risk category, which is why urine albumin-to-creatinine ratio matters alongside eGFR.

• When should I refer to nephrology?

  KDIGO guidelines recommend nephrology referral for: 1) eGFR <30 (CKD G4–G5), 2) Significant albuminuria (ACR >300 mg/g), 3) Rapid progression (eGFR decline >5 mL/min/year), 4) Persistent hematuria after urological evaluation, 5) Resistant hypertension (≥4 anti-hypertensives), 6) Persistent electrolyte abnormalities (hyperkalemia, metabolic acidosis), 7) Recurrent kidney stones, 8) Hereditary kidney disease suspected (polycystic kidney disease). Earlier referral (G3b) is recommended for complex patients. Timely referral to nephrology improves outcomes — late referral (first seen by nephrology <3 months before dialysis) is associated with increased mortality.