Race-free kidney function estimate. CKD-EPI 2021 equation.
What does eGFR mean?
Estimated Glomerular Filtration Rate (eGFR) is a calculated measure of how well the kidneys are filtering blood, expressed in mL per minute per 1.73m² of body surface area. Glomeruli are the tiny filtering units within the kidney; GFR measures the total volume of fluid filtered by all glomeruli per minute. A healthy person's kidneys filter approximately 90–120 mL of blood per minute.
This calculator uses the CKD-EPI 2021 equation (Inker et al., NEJM 2021), which replaced the earlier 2009 formula by removing the race coefficient. It uses serum creatinine, age, and sex to estimate GFR. The formula is validated in adults aged 18 and above.
Creatinine is a breakdown product of creatine phosphate in muscle. It is produced at a fairly constant rate and filtered by the kidneys. When kidney function declines, creatinine accumulates in the blood. The CKD-EPI equation converts this creatinine concentration into an estimated filtration rate, standardised to the average body surface area of 1.73m².
eGFR is used to stage chronic kidney disease (CKD) from G1 (normal) to G5 (kidney failure). It also guides drug dosing, many medications are renally cleared and require dose adjustment when eGFR falls below certain thresholds.
CKD stages by eGFR
| Stage | eGFR (mL/min/1.73m²) | Description |
|---|---|---|
| G1 — Normal | ≥ 90 | Normal or high function |
| G2 — Mildly reduced | 60 – 89 | Mildly reduced (common in older adults) |
| G3a — Mildly-moderately reduced | 45 – 59 | CKD if persists > 3 months |
| G3b — Moderately-severely reduced | 30 – 44 | Nephrology referral recommended |
| G4 — Severely reduced | 15 – 29 | Prepare for renal replacement therapy |
| G5 — Kidney failure | < 15 | Dialysis or transplant required |
When should you see a doctor?
A single eGFR below 60 should be repeated in 3 months. If it persists below 60, this meets the definition of chronic kidney disease and requires investigation. An eGFR that has dropped significantly from a previous measurement, or an eGFR below 30, warrants urgent nephrology review. Even mild CKD (G3) significantly increases cardiovascular risk and warrants optimisation of blood pressure, diabetes control, and avoidance of nephrotoxic drugs.