Creatinine Clearance Calculator (Cockcroft-Gault)

Calculator

How we calculate it

The Cockcroft-Gault equation estimates creatinine clearance as 140 minus age, multiplied by body weight in kilograms, divided by 72 times serum creatinine in mg/dL, with the result multiplied by 0.85 for women. It was published in 1976 from a study of 249 patients and predates the standardization of modern creatinine assays, which is why it tends to read higher than newer equations when applied to results from today’s laboratories. It remains in use because a great deal of renal drug dosing guidance was written against it, and substituting a different equation changes the number a dosing table was calibrated for. Which body weight belongs in the equation is genuinely unsettled: the original paper used actual weight, while many dosing references use ideal or adjusted body weight above a certain body size. This calculator reports the figure from the weight entered and, when a height is given, the same estimate recalculated from Devine ideal body weight alongside it, so the difference is visible rather than hidden in a single number. Creatinine clearance in mL/min is not the same quantity as eGFR in mL/min/1.73m², and the two are not interchangeable — eGFR is what current KDIGO guidance uses to stage kidney function.

Important limitations

• Cockcroft-Gault estimates clearance in mL/min and CKD-EPI estimates GFR in mL/min/1.73m². They are different quantities, they routinely disagree for the same blood test, and a figure from one cannot be read against the other’s categories.
• The equation was published in 1976 from 249 patients, with the factor for women added by adjustment. It predates modern creatinine assay standardization and tends to overestimate clearance when applied to results from today’s assays.
• Which body weight to use is unsettled. The original paper used actual weight; many dosing references use ideal or adjusted weight at higher body weights, and the choice changes the result substantially.
• Creatinine comes from muscle, so the estimate is unreliable at the extremes of muscle mass — in people who are very muscular, frail, malnourished, or after limb amputation.
• The equation assumes creatinine is in a steady state, so it is not valid during acute kidney injury or whenever kidney function is changing quickly, and it is not validated in pregnancy or in children.
• Where a drug label or protocol specifies a particular equation and weight basis, that specification is what applies. Dosing is a clinical decision, and this calculator is for understanding the number.
• One estimate from one blood test does not establish a diagnosis of any kidney condition.