Question 1

How is creatinine clearance calculated with the Cockcroft–Gault equation?

Accepted Answer

Cockcroft–Gault estimates creatinine clearance as ((140 − age) × weight in kg) ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for females. The result is an absolute clearance in mL/min. If creatinine is reported in µmol/L, it is divided by 88.42 to convert to mg/dL first. The equation was published by Cockcroft and Gault in 1976.

Question 2

What is the difference between creatinine clearance and eGFR?

Accepted Answer

Creatinine clearance (Cockcroft–Gault) estimates an absolute clearance in mL/min and is still used for many drug-dosing recommendations. eGFR equations such as CKD-EPI 2021 estimate glomerular filtration rate indexed to a standard body surface area of 1.73 m², in mL/min/1.73 m², and are used for diagnosing and staging chronic kidney disease. They are related but not interchangeable, especially at the extremes of body size.

Question 3

Which body weight should I use in Cockcroft–Gault?

Accepted Answer

The original equation was derived with actual (total) body weight. In practice, clinicians often use actual weight when a patient is at or below their ideal body weight, and ideal or adjusted body weight in obesity to avoid overestimating clearance. This calculator shows all three so you can compare, with ideal body weight from the Devine formula and adjusted weight as ideal + 0.4 × (actual − ideal).

Question 4

Why does this calculator support µmol/L and mg/dL?

Accepted Answer

Serum creatinine is reported in µmol/L in the UK and much of the world, and in mg/dL in the United States and some other countries. The conversion is 1 mg/dL = 88.42 µmol/L. Using the wrong units is a common source of error, so the calculator lets you enter creatinine in either unit and converts internally. Results are most accurate when the creatinine assay is standardised (IDMS-traceable).

Question 5

What are the KDIGO GFR categories?

Accepted Answer

KDIGO classifies GFR into six categories: G1 (≥90, normal or high), G2 (60–89, mildly decreased), G3a (45–59), G3b (30–44), G4 (15–29, severely decreased) and G5 (<15, kidney failure), all in mL/min/1.73 m². Categories G1 and G2 are only considered chronic kidney disease when there are additional markers of kidney damage, such as albuminuria.

Cockcroft–Gault · actual (80.0 kg)	87.3	mL/min
Cockcroft–Gault · ideal (70.5 kg)	76.9	mL/min
Cockcroft–Gault · adjusted (74.3 kg)	81.1	mL/min
Cockcroft–Gault · normalised	76.6	/1.73m²
CKD-EPI 2021 (eGFR)	84.4	/1.73m²