eGFR calculator (CKD-EPI 2021, race-free)
The CKD-EPI 2021 creatinine equation estimates your glomerular filtration rate (eGFR) — how much blood your kidneys filter each minute, scaled to a standard body size of 1.73 m2. Nephrologists, primary-care clinicians, and pharmacists use it to stage chronic kidney disease and flag reduced kidney function. It needs three inputs: age, sex, and a standardized serum creatinine level. This 2021 version is race-free and is the US standard endorsed by the NKF and ASN.
How it works
The equation takes your serum creatinine, divides it by a sex-specific constant K (0.7 female, 0.9 male), then applies one exponent when that ratio is at or below 1 and a steeper one (-1.200) when it is above 1 — capturing how filtering drops faster at higher creatinine. It then discounts for age and nudges up 1.2% for females. Full form: eGFR = 142 * min(SCr/K, 1)^A * max(SCr/K, 1)^(-1.200) * 0.9938^age * (1.012 if female), where A = -0.241 female, -0.302 male.
Worked example
Take a 55-year-old woman with a serum creatinine of 1.1 mg/dL. K = 0.7 and A = -0.241 (female). SCr/K = 1.1/0.7 = 1.571, so min(...,1) = 1 (contributes 1) and max(...,1) = 1.571. Then eGFR = 142 * 1 * 1.571^(-1.200) * 0.9938^55 * 1.012 = 142 * 0.5820 * 0.7115 * 1.012 = about 59 mL/min/1.73m2 — consistent with early-stage (G3a) reduced kidney function warranting follow-up.
Important
This tool provides an estimate only and is not a diagnosis or a substitute for professional clinical judgment. It uses the creatinine-only CKD-EPI 2021 equation; results can differ from cystatin C-based estimates and from the value your laboratory reports — always defer to your lab's reported eGFR and your clinician's interpretation. Accuracy depends on IDMS-standardized serum creatinine and a stable (non-acute) kidney state; results are unreliable in acute kidney injury, extremes of muscle mass (very high or very low), pregnancy, amputation, or severe illness, and this equation is validated for adults only (not those under 18). Any drug dosing decision must be confirmed by a licensed clinician or pharmacist. Do not start, stop, or change any medication based on this number.