eGFR calculator, CKD-EPI 2021.

How the 2021 CKD-EPI equation works

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^-1.200 × 0.9938^age × 1.012 if female. Scr is serum creatinine in mg/dL, κ is 0.7 for women and 0.9 for men, and α is -0.241 for women and -0.302 for men. The min and max terms mean the curve bends at a creatinine of κ: below it creatinine barely moves the estimate, above it the estimate falls steeply with an exponent of -1.200. The result is in mL/min per 1.73 m² of body surface area. This is the creatinine equation published by Inker and colleagues in the New England Journal of Medicine in 2021, and the one the National Kidney Foundation lists as the current race-free version.

The page you are on does the arithmetic in your browser and shows the one intermediate number worth checking, Scr divided by κ. If you have creatinine in umol/L, the calculator divides by 88.4 to get mg/dL first; that is the standard conversion between the two units, and the creatinine converter does only that step. The bands in the result follow the stage table on the National Kidney Foundation page listed under Sources: G1 is 90 or higher, G2 60 to 89, G3a 45 to 59, G3b 30 to 44, G4 15 to 29 and G5 below 15. The NKF notes that G1 and G2 count as kidney disease only when there are other signs of kidney damage, and that the numbers need to hold for 3 months or more.

Worked example

Woman, 60, creatinine 1.0 mg/dL. Scr/κ = 1.0 / 0.7 = 1.429. Because that is above 1, the min term is 1 and the max term is 1.429^-1.2 = 0.652. The age term is 0.9938⁶⁰ = 0.689. Then 142 × 0.652 × 0.689 × 1.012 = 64.5. For a man of the same age and creatinine, Scr/κ = 1.0 / 0.9 = 1.111, max term 1.111^-1.2 = 0.881, and 142 × 0.881 × 0.689 = 86.2. The two answers differ because the equation uses a different creatinine pivot for each sex, which reflects typical differences in creatinine production.

What this tool does not do: it does not adjust for unusual muscle mass, amputations, a creatine supplement or a very high-protein meal before the blood draw, any of which can move creatinine without changing the kidneys. It is for adults only and for a stable creatinine; it is not valid when kidney function is changing quickly, such as in acute illness. For drug dosing, many labels still use creatinine clearance; see the Cockcroft-Gault calculator, which answers a different question in different units.