Medical AICockcroft-Gault creatinine clearance calculator
The Cockcroft-Gault equation estimates creatinine clearance in mL/min from age, body weight, sex, and serum creatinine. It predates BSA-indexed eGFR equations and is not adjusted to 1.73m2, but it remains the estimate referenced in many drug labels, so it is still used for renal dose adjustment.
How to measure each input
- Age
- Current age in years. The numerator (140 - age) means clearance falls with age at any given creatinine.
- Weight
- The original study used actual body weight, but in obesity this over-estimates clearance. Many pharmacists use ideal body weight, or an adjusted body weight when actual exceeds ideal by more than 20 to 30 percent. Document which weight you used.
- Serum creatinine
- Use a steady-state serum creatinine in mg/dL (the calculator converts umol/L by dividing by 88.4). Some clinicians round very low creatinine values up in frail elderly patients to avoid over-estimating clearance, though this practice is debated.
- Sex
- Female estimates are multiplied by 0.85 to reflect lower average muscle mass.
Interpretation
| Band | Meaning |
|---|---|
| >= 50 mL/min | Generally consistent with standard dosing for most renally-cleared drugs, though individual labels set their own thresholds. Confirm against the specific product information. |
| 30 to 49 mL/min | Moderate impairment. Many drugs require a dose reduction or interval extension in this range. Check each renally-cleared agent against its label. |
| 15 to 29 mL/min | Severe impairment. Marked dose reduction or avoidance is common, and some agents are contraindicated. Review every renally-cleared and nephrotoxic drug. |
| < 15 mL/min or dialysis | Kidney failure range. Use dialysis-specific dosing where relevant and avoid agents that accumulate. Many drugs need supplemental dosing after hemodialysis. |
Pitfalls, exclusions and caveats
- The choice of body weight materially changes the result. Actual weight over-estimates clearance in obesity; consider ideal or adjusted body weight. In amputees, use a corrected weight.
- Edema and ascites inflate measured weight without adding muscle, so actual weight over-estimates clearance in fluid-overloaded patients.
- Cockcroft-Gault gives an absolute clearance in mL/min and is not indexed to 1.73m2 body surface area, so it is not directly interchangeable with eGFR for staging CKD.
- Like all creatinine-based estimates it assumes steady state and is invalid in acute kidney injury or rapidly changing creatinine.
- It systematically over-estimates true GFR because creatinine is also secreted by the tubules; this was partly by design, since it was fitted to clearance not GFR.
CrCl (mL/min) = ((140 - age) x weight_kg) / (72 x Scr_mg/dL), then x 0.85 if female. Result is an absolute clearance in mL/min, not indexed to body surface area.The Cockcroft-Gault equation was published by Cockcroft and Gault (1976). This implementation is an educational tool and is not affiliated with the original authors or any regulatory body.
Frequently asked
Should I use Cockcroft-Gault or eGFR for drug dosing?
Use whichever the specific drug label or dosing reference was built on. Many older and some newer labels specify Cockcroft-Gault creatinine clearance, so substituting a BSA-indexed eGFR can change the dose band. When in doubt, follow the product information.
Which weight should I enter for an obese patient?
Actual body weight over-estimates clearance in obesity. A common approach is ideal body weight, or an adjusted body weight when actual exceeds ideal by more than 20 to 30 percent. The right choice can be drug-specific, so document the weight you used.
Why is Cockcroft-Gault not indexed to 1.73m2?
It was derived to predict measured creatinine clearance in mL/min, not a BSA-standardised GFR. That is why its output is an absolute clearance and why it is not directly interchangeable with eGFR for CKD staging.
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