Cockcroft-Gault Creatinine Clearance Calculator
Cockcroft-Gault Creatinine Clearance Calculator
Estimate creatinine clearance in mL/min — the equation most drug labels specify for renal dose adjustment.
Cockcroft-Gault Creatinine Clearance
Drug dosing equationMale, age 62, weight 72 kg, creatinine 1.3 mg/dL
Formula
- age
- years
- weight
- kg — see the guidance below on actual, ideal and adjusted body weight
- Scr
- serum creatinine in mg/dL
- 0.85
- the female factor, reflecting lower average muscle mass
- result
- mL/min — an absolute clearance, not indexed to body surface area
Worked example
Male, age 62, weight 72 kg, creatinine 1.3 mg/dL
(140 − 62) × 72 = 5616
72 × 1.3 = 93.6
5616 ÷ 93.6 = 60.0 mL/min
Which weight to use
| Body habitus | Weight to use |
|---|---|
| Normal weight | Actual body weight |
| Underweight (actual below ideal) | Actual body weight |
| Obese (over about 120% of ideal) | Adjusted body weight = IBW + 0.4 × (actual − IBW) |
| Amputation, oedema, ascites | Estimate lean weight; interpret cautiously |
Why an obsolete equation is still the standard for dosing
Cockcroft-Gault dates from 1973, was derived in 249 men, and estimates creatinine clearance rather than GFR — a quantity that exceeds true GFR because creatinine is secreted by the tubules as well as filtered. By every measure of accuracy it is inferior to CKD-EPI. It nonetheless remains the equation most drug labels specify, because the pharmacokinetic studies underpinning renal dose adjustment were performed using it, and the dosing thresholds printed on labels are Cockcroft-Gault thresholds.
Using a different equation to apply those thresholds introduces a mismatch. The difference is usually small but not always, and it matters most in the patients where dosing errors are most consequential: the elderly, the obese, and those near a cut-off such as the 30 mL/min threshold for direct oral anticoagulants.
The other reason it survives is that it produces an absolute clearance in mL/min, which is what dosing needs. Reported eGFR is indexed to 1.73 m² of body surface area, and in a 120 kg patient the indexed and absolute values differ by 30% or more. Using an indexed eGFR to make a dosing decision in a large person systematically under-doses them.
The weight to enter is genuinely contested. Most institutions use actual body weight in normal-weight patients and adjusted body weight in obesity; the important thing is to apply one convention consistently and record which.
Frequently asked questions
Which weight should I use in Cockcroft-Gault?
Actual body weight for normal-weight and underweight patients, and adjusted body weight — ideal plus 40% of the excess — for obese patients. Conventions differ between institutions, so apply one consistently.
Why do drug labels still use Cockcroft-Gault?
The pharmacokinetic studies behind renal dose adjustment were done using it, so the thresholds printed on labels are Cockcroft-Gault thresholds. Applying them to a CKD-EPI value introduces a mismatch.
What is the difference between creatinine clearance and eGFR?
Creatinine clearance exceeds true GFR because creatinine is secreted by the tubules as well as filtered. Cockcroft-Gault also returns an absolute clearance in mL/min, while eGFR is indexed to 1.73 m² of body surface area.
Can I use eGFR for drug dosing instead?
Only after de-indexing it — multiply by the patient’s body surface area and divide by 1.73. Using the indexed value directly under-doses large patients and over-doses small ones.
Related calculators
References
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31–41.
- US FDA. Guidance for Industry: pharmacokinetics in patients with impaired renal function.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.