GFR calculator

How this calculator works

Choose the markers actually measured. Current creatinine and combined estimates use the race-free 2021 equations; cystatin C alone uses the 2012 equation. Use IDMS-traceable creatinine and standardised cystatin C assays in adults. Historical comparisons retain each original coefficient, including the original race term, and are not the current default. Results are indexed to 1.73 m². Acute changes, pregnancy and unusual muscle mass can make estimates misleading; one result cannot establish chronic kidney disease. The result is an estimate for information only and is not medical advice.

Formula

Let r = serum creatinine (mg/dL)/k, k = 0.7 female or 0.9 male; s = cystatin C (mg/L)/0.8. CKD-EPI 2021 creatinine = 142 × min(r,1)^a × max(r,1)^-1.200 × 0.9938^age × (1.012 if female), a = -0.241 female or -0.302 male. Combined 2021 = 135 × min(r,1)^b × max(r,1)^-0.544 × min(s,1)^-0.323 × max(s,1)^-0.778 × 0.9961^age × (0.963 if female), b = -0.219 female or -0.144 male. Cystatin 2012 = 133 × min(s,1)^-0.499 × max(s,1)^-1.328 × 0.996^age × (0.932 if female). Original 2009 creatinine uses 141, a = -0.329 female/-0.411 male, high exponent -1.209, 0.993^age, female 1.018, Black 1.159. IDMS MDRD = 175 × creatinine^-1.154 × age^-0.203 × (0.742 if female) × (1.212 if Black). Combined 2012 uses 135, a = -0.248 female/-0.207 male, high creatinine exponent -0.601, cystatin exponents -0.375 and -0.711, 0.995^age, female 0.969 and Black 1.08.

Worked example

For a 60-year-old man with creatinine 0.9 mg/dL, r = 1 and the 2021 creatinine result is 142 × 0.9938^60 = 97.7750 mL/min/1.73 m². At the same age, a woman with creatinine 0.7 mg/dL gives 98.9483.

Frequently asked questions

Sources

• Inker et al. (2021): original race-free equations
• Inker et al. (2012): original cystatin and combined equations, Table 2 footnotes
• Levey et al. (2009): original CKD-EPI creatinine equation
• Levey et al. (2006): standardised MDRD equation
• NIDDK: adult eGFR equations and assays