Creatinine clearance calculator (Cockcroft–Gault)
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Result
An estimate for exam practice only. Cockcroft–Gault estimates creatinine clearance, not GFR, and is not valid in unstable kidney function, pregnancy, extremes of body size or children. Never base a real dose on this result.
Estimate creatinine clearance with the Cockcroft–Gault equation, as used in pharmacology exam questions about renal dose adjustment. Enter the age, sex, weight and serum creatinine (in mg/dL or µmol/L) and choose actual, ideal or adjusted body weight. Every step is shown: the unit conversion, the Devine ideal body weight and the equation itself. This is an estimate for exam practice only, never a basis for a real dose.
Step-by-step solution
Cockcroft–Gault equation
Key formulas
- Cockcroft–Gault
- CrCl = (140 − age) × kg ÷ (72 × SCr in mg/dL), × 0.85 for women
- Creatinine units
- 1 mg/dL = 88.4 µmol/L
How to calculate creatinine clearance with Cockcroft–Gault
- Convert the serum creatinine to mg/dL if it is given in µmol/L: divide by 88.4.
- Choose the weight. Many exam questions use the actual weight; for obese patients the ideal or adjusted body weight is often used instead.
- Ideal body weight (Devine): 50 kg for men or 45.5 kg for women, plus 2.3 kg for every inch of height above 5 feet. Adjusted body weight = IBW + 0.4 × (actual − IBW).
- Apply CrCl = (140 − age) × weight / (72 × serum creatinine), with the weight in kg and the creatinine in mg/dL.
- For a woman, multiply the result by 0.85.
Questions and answers
Is creatinine clearance the same as GFR?
No. Cockcroft–Gault estimates creatinine clearance in mL/min, which overestimates the true GFR because some creatinine is secreted by the tubules. Laboratories usually report an eGFR from the CKD-EPI equation, in mL/min/1.73 m².
Why is the factor 0.85 used for women?
Women have on average less muscle mass, so they produce less creatinine for the same kidney function. The original 1976 study applied an estimated 15% reduction.
Which weight should I use in exam questions?
Use the weight the question asks for. A common textbook convention is the actual weight when it is below the ideal weight, the ideal weight for normal-weight patients, and the adjusted weight for obese patients, but references differ.
How do I convert µmol/L to mg/dL?
Divide by 88.4. A serum creatinine of 106 µmol/L is 106/88.4 = 1.20 mg/dL.
When is Cockcroft–Gault unreliable?
When kidney function is changing quickly, in very old or very muscular or very thin patients, in amputees, in pregnancy and in children. In those situations the estimate can be far off.