GFR Calculator (Kidney Function)
Estimate glomerular filtration rate (eGFR) using the CKD-EPI equation.
Enter age, serum creatinine, and sex to assess kidney function stage.
Glomerular Filtration Rate (GFR) measures how well your kidneys filter waste from your blood. It is reported as eGFR (estimated GFR) because direct measurement is impractical outside of research settings.
CKD-EPI Formula (2021, current standard — no race variable):
For creatinine in mg/dL:
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.200) × 0.9938^Age
Then multiply by 1.012 for females.
Where:
- Scr = serum creatinine (mg/dL)
- κ = 0.7 for females, 0.9 for males
- α = −0.241 for females, −0.302 for males
Simplified older MDRD formula (still widely reported):
eGFR = 175 × Scr^(−1.154) × Age^(−0.203) × (0.742 if female)
Worked example (CKD-EPI simplified): Male, age 55, serum creatinine = 1.3 mg/dL Scr/κ = 1.3 / 0.9 = 1.44 (greater than 1, so use the max term only) eGFR ≈ 142 × (1.44)^(−1.200) × 0.9938^55 ≈ ~58 mL/min/1.73 m²
CKD Staging by eGFR:
| Stage | eGFR | Description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderate |
| G3b | 30–44 | Moderate to severe |
| G4 | 15–29 | Severely decreased |
| G5 | <15 | Kidney failure |
eGFR naturally declines with age — after age 40, eGFR drops ~1 mL/min/1.73m² per year even in healthy people. A single low reading requires follow-up; diagnosis of CKD requires persistence over 3+ months.