Creatinine clearance: the Cockcroft-Gault equation explained
Cockcroft-Gault is the standard formula used for drug dosing in renal impairment. Published in 1976, it calculates an estimated creatinine clearance from 4 variables: age, sex, weight and serum creatinine. The National Kidney Foundation notes it has been used for nearly 50 years to inform medication dosing in kidney disease.
The formula
CrCl (mL/min) = ((140 - age) × weight in kg) / (72 × serum creatinine in mg/dL), multiplied by 0.85 for female patients. The female correction accounts for lower muscle mass and therefore lower baseline creatinine production. The formula predates modern lab standardisation: serum creatinine assays weren't standardised when Cockcroft-Gault was published in 1976, and the FDA's 2024 guidance for industry now recommends eGFR over CrCl when studying a new drug's pharmacokinetics in renal impairment.
Which weight to use
For patients whose actual body weight is close to their ideal body weight, use actual weight. For obese patients (actual weight significantly exceeds IBW), use IBW instead, otherwise CrCl is overestimated. Use our Ideal Body Weight Calculator if needed, then carry that same weight logic into our Weight-Based Dosage Calculator to work out the actual drug dose once you have a CrCl.
CrCl vs eGFR
Cockcroft-Gault CrCl and CKD-EPI eGFR are different calculations, and pharmacy practice is currently mid-shift between them. For decades CrCl was preferred for drug dosing because most existing renal dosing guidelines and drug labels were built from Cockcroft-Gault data. That is changing: the National Kidney Foundation now recommends moving away from Cockcroft-Gault toward race-agnostic, BSA-adjusted eGFR for medication-related decisions, since the original 1976 data came from only 249 white male patients and creatinine assays have since been re-standardised, and the FDA's 2024 guidance points the same direction for new drugs. Until individual drug labels and your institution's protocols catch up with that shift, this calculator gives you the Cockcroft-Gault value that most current dosing references still specify. Use our Renal Dose Adjustment Calculator alongside this result, and check whether the specific drug's label has already moved to eGFR-based dosing.