Estimation of creatinine clearance (CrCl) for drug dose adjustment.

What it is and when to use it

The Cockcroft-Gault calculator estimates creatinine clearance (CrCl) in mL/min from a patient's age, weight, sex and serum creatinine, and is mainly used for drug dose adjustment in renal impairment. Cockcroft and Gault published the formula in Nephron in 1976: CrCl = (140 − age) × weight (kg) / (72 × serum creatinine in mg/dL), with a result 15% lower in women (factor 0.85). It was set out for adult men, based on the relationship between age and 24-hour urinary creatinine excretion per kg of body weight in 249 patients aged 18 to 92 years. Against the mean of two measured 24-hour clearances in 236 patients, the correlation coefficient between predicted and measured values was 0.83.

How to interpret it

The result is an absolute clearance in mL/min, not indexed to 1.73 m² of body surface area, because weight is already in the formula. The page sorts the result into five bands: ≥90 mL/min, normal; 60–89, mild renal impairment; 30–59, moderate, where renally excreted drugs usually need a lower dose or a longer interval; 15–29, severe; and <15 mL/min, renal failure. These bands do not come from the 1976 paper: they mirror the glomerular filtration rate cut-offs used to stage chronic kidney disease. When prescribing, what counts is each drug's own threshold in its product information, not the label of the band.

Limitations and when not to use it

The formula assumes a stable serum creatinine: in acute kidney injury, while creatinine is changing, it does not reflect true function. It uses the weight entered without correction, so it may overestimate clearance in marked obesity, oedema or very low muscle mass (cachexia, amputation). For women the paper proposes a result 15% lower, and the abstract does not explain how that correction was obtained. The equation predates IDMS-traceable creatinine standardisation, so modern assays may give somewhat different values. The calculator accepts creatinine in mg/dL only (µmol/L ÷ 88.4) and ages from 18 years.

Frequently asked questions

How do you calculate creatinine clearance with Cockcroft-Gault?

Subtract age from 140, multiply by weight in kg, and divide by 72 times creatinine in mg/dL; in women, multiply the result by 0.85. A 70-year-old man weighing 70 kg with creatinine 1.0 mg/dL has 68.1 mL/min.

What is the difference between Cockcroft-Gault and CKD-EPI 2021?

Cockcroft-Gault estimates creatinine clearance in mL/min and includes body weight. CKD-EPI 2021 estimates glomerular filtration rate normalised to a standard body surface area and is the equation laboratories usually report for staging chronic kidney disease. For drug dosing, follow the product information.

Which weight should be used in Cockcroft-Gault for obese patients?

The calculator uses the weight you enter; the paper's abstract refers to weight in kg and does not mention ideal or adjusted body weight. In marked obesity, actual weight overestimates clearance, and many clinicians use ideal or adjusted weight instead.

Is Cockcroft-Gault used for drug dose adjustment in renal impairment?

That is its main use: much of the renal dosing guidance in product information is expressed as creatinine clearance estimated with this formula. Before changing a dose, check the drug's own threshold and confirm that creatinine is stable.