eGFR Kidney Function: The CKD-EPI Formula, Worked Examples, and Stages
October 29, 2026
The estimated glomerular filtration rate (eGFR) is the standard estimate of how well the kidneys filter blood. It is calculated from serum creatinine, age, and sex. The 2021 CKD-EPI equation (without a race coefficient) is: eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 [if female], where Scr is creatinine in mg/dL, κ is 0.7 for females and 0.9 for males, and α is −0.241 for females and −0.302 for males.
The units are mL/min/1.73 m². Creatinine is a waste product of muscle metabolism, and its blood level rises as filtration falls.
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Man, 50, creatinine 1.0: Scr/κ = 1.111; the min term is 1, the max term 1.111^−1.2 = 0.881, and 0.9938^50 = 0.733. eGFR = 142 × 0.881 × 0.733 = 91.7, or about 92. Woman, 60, creatinine 0.9: Scr/κ = 1.286; 1.286^−1.2 = 0.740; 0.9938^60 = 0.689; eGFR = 142 × 0.740 × 0.689 × 1.012 = 73.2. Man, 70, creatinine 1.5: Scr/κ = 1.667; 1.667^−1.2 = 0.542; 0.9938^70 = 0.647; eGFR = 142 × 0.542 × 0.647 = 49.8, or about 50. The same creatinine can imply different eGFR values at different ages: kidney function declines slowly with age.
| Person | Creatinine (mg/dL) | eGFR | Stage |
|---|---|---|---|
| Man, 50 | 1.0 | 92 | G1 |
| Woman, 60 | 0.9 | 73 | G2 |
| Man, 70 | 1.5 | 50 | G3a |
| Man, 30 | 0.8 | 122 | G1 |
| Woman, 65 | 2.5 | 21 | G4 |
CKD Stages
G1: 90 or higher (normal or high, with other signs of kidney damage for a diagnosis). G2: 60 to 89 (mildly decreased). G3a: 45 to 59 (mild to moderate decrease). G3b: 30 to 44 (moderate to severe decrease). G4: 15 to 29 (severely decreased). G5: below 15 (kidney failure). Chronic kidney disease is diagnosed when abnormal kidney function or structure persists for at least 3 months. The urine albumin-to-creatinine ratio is also part of staging.
Limits of the Estimate
eGFR is an estimate. Very muscular or very frail people, vegetarians, people taking creatine supplements, and eating a large amount of cooked meat before the test can have creatinine levels that make eGFR less reliable. Cystatin C-based equations may be used to confirm. Dehydration and certain medications can temporarily change creatinine. Always interpret results with a clinician, who will repeat tests and look at the trend.
Protecting Kidney Function
Blood pressure and blood sugar control are the main levers, along with avoiding long-term heavy use of NSAID painkillers, not smoking, staying hydrated, and maintaining a healthy weight. People with diabetes, hypertension, or a family history of kidney disease are typically screened yearly. This article is educational; it does not replace medical advice.
Frequently Asked Questions
What does eGFR measure?
An estimate of how well the kidneys filter blood, in mL/min/1.73 m².
What inputs does CKD-EPI use?
Serum creatinine, age, and sex.
What eGFR indicates kidney failure?
Below 15.
Can eGFR be unreliable?
Yes, in people with unusual muscle mass or diet, among other factors.
How is CKD diagnosed?
Abnormal function or markers lasting at least 3 months.