Classic equation for drug-dose adjustment.
Source: Cockcroft & Gault, Nephron 1976.
What does creatinine clearance mean?
Creatinine clearance (CrCl) is a measure of how efficiently the kidneys clear creatinine from the blood, expressed in mL per minute. It is an approximation of the glomerular filtration rate, the fundamental measure of kidney function. Unlike eGFR (which is normalised to 1.73m² BSA), CrCl is an absolute value that depends on body size.
The Cockcroft-Gault equation, published in Nephron in 1976, estimates CrCl from age, weight, sex, and serum creatinine. The formula uses actual body weight for the calculation. For obese patients, many clinicians substitute ideal body weight or adjusted body weight to avoid overestimating renal function.
The primary use of Cockcroft-Gault today is in drug dosing. Most pharmaceutical prescribing information was written using CrCl calculated by this formula, and regulatory bodies such as the FDA and EMA continue to reference it. Drugs that are predominantly renally cleared, including many antibiotics (aminoglycosides, vancomycin), anticoagulants (dabigatran), and chemotherapy agents, require dose adjustments based on CrCl thresholds.
Cockcroft-Gault was derived from a mostly male cohort studied in the 1970s, so it can be biased in some populations. For staging kidney disease, eGFR (CKD-EPI) is now the preferred measure. CrCl by Cockcroft-Gault is primarily retained for its historical role in drug development databases.
Reference ranges
| CrCl (mL/min) | Renal function | Drug dosing implication |
|---|---|---|
| ≥ 90 | Normal | Full dose for most renally cleared drugs |
| 60 – 89 | Mildly reduced | Monitor; dose reduction for some drugs |
| 30 – 59 | Moderately reduced | Dose reduction required for many drugs |
| 15 – 29 | Severely reduced | Major dose adjustments or drug avoidance |
| < 15 | Kidney failure | Many drugs contraindicated |
When should you see a doctor?
A declining or low CrCl is a medical concern requiring evaluation, particularly if you are taking renally cleared medications. If your CrCl is below 60 mL/min, inform all prescribing clinicians so they can review your medication doses. Do not adjust prescribed medications based on this calculator without consulting your doctor or pharmacist.
Frequently asked questions
What is the Cockcroft-Gault formula?
The Cockcroft-Gault equation estimates creatinine clearance as: CrCl (mL/min) = [(140 − age) × weight kg] / (72 × serum creatinine mg/dL), multiplied by 0.85 for women. In SI units (creatinine in µmol/L): CrCl = [(140 − age) × weight kg × 1.23 (men) or 1.04 (women)] / creatinine µmol/L. It was published in 1976 and remains the formula most drug regulatory agencies use for prescribing information.
Why use Cockcroft-Gault instead of eGFR?
Most drug prescribing information and clinical trials used CrCl estimated by Cockcroft-Gault rather than eGFR to determine dose adjustments. The two are related but not identical. CrCl is not standardised to body surface area, meaning a large person gets a higher CrCl than a small person with the same renal function. For drug dosing, this un-standardised value is often more appropriate because drug distribution also relates to body size.
Which weight should I use for Cockcroft-Gault?
For patients with normal weight or who are underweight, use actual body weight. For obese patients (BMI > 30), guidelines vary: some recommend ideal body weight (IBW), others use adjusted body weight (ABW = IBW + 0.4 × (actual weight − IBW)), because creatinine clearance scales primarily with lean mass. Using actual body weight in obese patients tends to overestimate CrCl.