Health & Medicine · Pharmacokinetics
eGFR Calculator (CKD-EPI)
Estimates glomerular filtration rate using the 2021 CKD-EPI creatinine equation to stage chronic kidney disease.
Calculator
Formula
For females: \kappa = 0.7,\ \alpha = -0.241; for males: \kappa = 0.9,\ \alpha = -0.302. S_{cr} is serum creatinine in mg/dL. The exponent applied is \alpha when S_{cr}/\kappa < 1, and -1.200 when S_{cr}/\kappa \geq 1. A sex multiplier of 1.012 is applied for females.
Source: Inker LA et al. (2021). New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. NEJM 385:1737–1749.
How it works
The CKD-EPI equation uses serum creatinine, age, and biological sex to estimate GFR. Creatinine is a muscle waste product filtered by the kidneys; higher serum levels indicate reduced filtration. The equation applies sex-specific constants (κ and α) because men and women differ in average muscle mass, which affects baseline creatinine production.
The result is classified into CKD stages: G1 (≥90, normal or high), G2 (60–89, mildly decreased), G3a (45–59), G3b (30–44), G4 (15–29, severely decreased), and G5 (<15, kidney failure). Drug dosing, contrast media decisions, and transplant eligibility are all guided by eGFR.
Worked example
A 58-year-old male has a serum creatinine of 1.4 mg/dL.
κ = 0.9 (male), α = −0.302. Ratio = 1.4 / 0.9 = 1.556 ≥ 1, so we use the high branch: (1.556)^(−1.200) = 0.597. Age factor: 0.9938^58 = 0.699. Sex multiplier = 1.0 (male).
eGFR = 142 × 0.597 × 0.699 × 1.0 ≈ 59.3 mL/min/1.73 m² → CKD Stage G3a (mildly to moderately decreased).
Limitations & notes
The CKD-EPI equation performs best in stable outpatients and is less accurate in acute kidney injury, extreme muscle mass (bodybuilders, amputees, severe malnutrition), pregnancy, and ages under 18. It assumes steady-state creatinine and may underestimate true GFR in individuals with high dietary protein or creatine supplementation. Cystatin C-based or combined creatinine–cystatin C equations may be preferred when accuracy is critical.
Frequently asked questions
What is a normal eGFR?
An eGFR of 60 mL/min/1.73 m² or above is generally considered within the acceptable range for most adults. Values consistently below 60 for more than 3 months indicate chronic kidney disease.
Why does eGFR decline with age?
Kidney function naturally decreases with age due to nephron loss and reduced renal blood flow. An eGFR of around 75 in a healthy 75-year-old may reflect normal aging rather than disease.
How does this differ from creatinine clearance (Cockcroft-Gault)?
CKD-EPI estimates GFR normalized to body surface area and is more accurate across a wider range of kidney function. Cockcroft-Gault estimates absolute creatinine clearance (mL/min) and is still widely used for drug dosing.
Why was race removed from the 2021 equation?
The original 2009 CKD-EPI equation included a race coefficient for Black patients, which was criticized for lacking biological justification and potentially delaying diagnosis. The 2021 revision removed race to improve equity and universal applicability.
Can I use this calculator for children?
No — CKD-EPI is validated for adults aged 18 and older. The Schwartz equation is used to estimate GFR in pediatric patients.
Last updated: 2025-01-15 · Formula verified against primary sources.