What is eGFR and why does it matter?

eGFR (estimated glomerular filtration rate) measures how well your kidneys filter waste from the blood, expressed in mL/min per 1.73 m² of body surface area. A healthy young adult has an eGFR above 90. Values persistently below 60 for more than three months indicate chronic kidney disease (CKD), which affects drug dosing, cardiovascular risk, and long-term health planning.

What is the CKD-EPI 2021 equation?

CKD-EPI 2021 is the current gold-standard equation endorsed by KDIGO, NKF, and ASN. Published by Inker et al. in NEJM 2021, it removed the race adjustment from the 2009 version. The formula is: eGFR = 142 x min(Scr/kappa, 1)^alpha x max(Scr/kappa, 1)^(-1.2) x 0.9938^Age x sex-factor. For females: kappa = 0.7, alpha = -0.241, sex-factor = 1.012. For males: kappa = 0.9, alpha = -0.302, sex-factor = 1.0. Serum creatinine is in mg/dL.

How is Cockcroft-Gault creatinine clearance different from CKD-EPI eGFR?

Cockcroft-Gault (1976) estimates creatinine clearance (CrCl) in mL/min using age, weight, sex, and serum creatinine without adjusting for body surface area. It is still widely used for drug dosing calculations because most pharmacokinetic studies were validated against it. CKD-EPI eGFR is preferred for CKD diagnosis and staging. The two values can diverge in patients who are very muscular, very obese, or at extremes of body size.

What do the CKD stages mean?

KDIGO 2022 defines six GFR stages. G1 (eGFR 90+) is normal or high. G2 (60-89) is mildly decreased. G3a (45-59) is mild-to-moderately decreased. G3b (30-44) is moderately-to-severely decreased. G4 (15-29) is severely decreased. G5 (below 15) indicates kidney failure. CKD requires a GFR below 60 or kidney damage persisting more than three months. If your calculated eGFR is below 60, consult your GP or nephrologist.

Does the 2021 equation remove race as a variable?

Yes. The 2021 update removed the race coefficient from the 2009 equation. The previous race adjustment resulted in systematic under-diagnosis of CKD in Black individuals. The 2021 equation uses only age, sex, and serum creatinine, and performs at least as well across all racial and ethnic groups in the validation cohort.

Should I use mg/dL or µmol/L?

Both are accepted. UK and European labs typically report in µmol/L; US labs report in mg/dL. Select your units and the calculator converts automatically using the factor 1 mg/dL = 88.42 µmol/L. A typical normal range is roughly 0.7-1.2 mg/dL (62-106 µmol/L) for men and 0.5-1.0 mg/dL (44-88 µmol/L) for women, though reference ranges vary by laboratory.

eGFR Calculator (CKD-EPI 2021)

An eGFR calculator built on the latest CKD-EPI 2021 (race-free) equation — the standard now recommended by KDIGO, the National Kidney Foundation, and the American Society of Nephrology. Enter your age, biological sex, and serum creatinine to get your estimated glomerular filtration rate (eGFR), a Cockcroft-Gault creatinine clearance for comparison, and your KDIGO 2022 CKD stage on a colour-coded spectrum bar. It runs entirely in your browser — nothing is uploaded or stored.

This tool is for educational purposes only and does not constitute medical advice. A single eGFR value is not sufficient for diagnosis. Always have kidney function interpreted by a qualified clinician before making any treatment or dosing decisions.

How it works

The 2021 CKD-EPI equation (Inker et al., NEJM 2021, doi:10.1056/NEJMoa2102953) estimates GFR from serum creatinine, age, and sex alone — the race coefficient from the 2009 version was removed after it was shown to cause systematic CKD under-diagnosis in Black patients.

The formula (serum creatinine in mg/dL):

eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.2) × 0.9938^Age × S

Where the constants differ by sex:

Sex	κ (kappa)	α (alpha)	S (sex factor)
Female	0.7	-0.241	1.012
Male	0.9	-0.302	1.000

The min and max terms model the non-linear relationship between creatinine and GFR below and above the κ threshold. Below κ the curve is less steep — creatinine can vary widely at normal GFR. Above κ it is steeper, tracking falling GFR more reliably. The 0.9938^Age term captures the gradual age-related GFR decline even when creatinine remains stable.

The tool also computes Cockcroft-Gault creatinine clearance (CrCl):

CrCl = ((140 − Age) × Weight_kg) / (72 × Scr_mg/dL)   [× 0.85 if female]

CrCl is not adjusted for body surface area and uses body weight, so it remains the formula of choice for dosing renally-cleared drugs (e.g., aminoglycosides, digoxin, direct oral anticoagulants).

CKD staging follows KDIGO 2022 GFR categories:

Stage	eGFR (mL/min/1.73m²)	Description
G1	90+	Normal or high
G2	60-89	Mildly decreased
G3a	45-59	Mild-to-moderately decreased
G3b	30-44	Moderately-to-severely decreased
G4	15-29	Severely decreased
G5	below 15	Kidney failure

Note that CKD requires the reduced GFR (or evidence of kidney damage) to persist for more than three months — a single measurement is not diagnostic.

Worked example

A 55-year-old male with a serum creatinine of 1.1 mg/dL and body weight of 75 kg:

CKD-EPI 2021 step by step:

kappa = 0.9, alpha = -0.302
Scr/kappa = 1.1 / 0.9 = 1.222 (greater than 1)
min(1.222, 1)^(−0.302) = 1.0 (ratio capped at 1)
max(1.222, 1)^(−1.2) = 1.222^(−1.2) = approximately 0.8168
Age factor: 0.9938^55 = approximately 0.7097
eGFR = 142 × 1.0 × 0.8168 × 0.7097 × 1.0 = 82.4 mL/min/1.73m² — Stage G2

Cockcroft-Gault:

CrCl = ((140 − 55) × 75) / (72 × 1.1) = 6375 / 79.2 = 80.5 mL/min

Both values land in the mildly-decreased range. At creatinine 1.8 mg/dL (same patient), the eGFR drops to approximately 47 mL/min/1.73m² — Stage G3a — flagging clinically important renal impairment requiring medication review and nephrology referral per KDIGO guidelines.

Age	Sex	Creatinine (mg/dL)	eGFR (approx.)
40	F	0.8	96 (G1)
55	M	1.1	82 (G2)
65	F	1.4	48 (G3a)
70	M	2.2	29 (G4)

Every figure is calculated in your browser — no data is uploaded or stored anywhere.