How do you calculate creatinine clearance?
The Cockcroft-Gault equation, published in 1976, estimates how many millilitres of plasma are cleared of creatinine each minute. Creatinine must be in mg/dL, so a value in µmol/L is divided by 88.4 first.
CrCl (mL/min) = (140 − age) × weight (kg) ÷ (72 × creatinine mg/dL) × 0.85 if female
Older age, lower weight and higher creatinine all lower the result. Unlike eGFR, the answer is not indexed to body surface area. It is an absolute value in mL/min, rounded to a whole number.
How to use the creatinine clearance calculator
- Enter the Age in years.
- Choose the Sex. For females the result is multiplied by 0.85.
- Enter the Weight in kg. It’s worth checking which weight the drug information or local protocol asks for: actual, ideal or adjusted.
- Pick the Creatinine unit (µmol/L or mg/dL) and enter the Serum creatinine.
- Read the CrCl in mL/min and follow the working underneath.
Worked examples
Example 1 – creatinine in mg/dL. A man aged 70, 80 kg, creatinine 1.2 mg/dL. (140 − 70) × 80 = 5600. 72 × 1.2 = 86.4. 5600 ÷ 86.4 = 65 mL/min.
Example 2 – a small, older woman. A woman aged 85, 50 kg, creatinine 0.9 mg/dL. (140 − 85) × 50 = 2750. 72 × 0.9 = 64.8. 2750 ÷ 64.8 = 42.4, then × 0.85 = 36 mL/min. A “normal” creatinine hides a clearly reduced clearance here.
Example 3 – creatinine in µmol/L. A man aged 60, 72 kg, creatinine 88 µmol/L. 88 ÷ 88.4 = 0.995 mg/dL. (140 − 60) × 72 = 5760. 72 × 0.995 = 71.67. 5760 ÷ 71.67 = 80 mL/min.
How age changes the result
CrCl for a 70 kg adult with the same creatinine of 1.0 mg/dL (88.4 µmol/L). The blood test is identical, yet the estimated clearance halves between 40 and 90 years.
| Age | Male | Female |
|---|---|---|
| 40 years | 97 mL/min | 83 mL/min |
| 60 years | 78 mL/min | 66 mL/min |
| 80 years | 58 mL/min | 50 mL/min |
| 90 years | 49 mL/min | 41 mL/min |
Common mistakes
- Mixing up the creatinine unit. 88 µmol/L entered as 88 mg/dL gives a CrCl of about 1 mL/min. The reverse, 1.2 mg/dL entered as µmol/L, gives thousands of mL/min. It’s advisable to check the unit on the lab report every time.
- Using the wrong weight. In obesity, actual weight can overestimate clearance considerably. It’s best to use the weight your drug information specifies. The ideal body weight and adjusted body weight calculators give you the alternatives.
- Swapping CrCl and eGFR. A label that says “CrCl 30–50 mL/min” refers to Cockcroft-Gault, not to the eGFR printed on the lab report. Our guide to eGFR vs creatinine clearance explains the difference.
- Forgetting the 0.85 factor for women, which changes the result by 15%.
When the estimate is unreliable
- Unstable creatinine. In acute kidney injury, or when creatinine is rising or falling quickly, the equation does not reflect current function.
- Low muscle mass. Frail older people, amputees and people who have been bedbound for a long time produce little creatinine. A “normal” creatinine can then hide poor clearance. Some local policies round very low creatinine values up before calculating; practice varies.
- Extremes of weight and fluid status. Oedema, ascites and obesity add weight that does not produce creatinine.
- Modern laboratory methods. The equation was derived with older creatinine assays. Today’s standardised assays read slightly lower, which pushes CrCl up.
- Pregnancy and children, for whom the equation was not designed.
When the result guides a drug dose, we recommend checking it against the product information and your local protocol.
Frequently asked questions
What is the Cockcroft-Gault formula?
CrCl = (140 − age) × weight in kg ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for women. The result is in mL/min. A 70-year-old man weighing 80 kg with a creatinine of 1.2 mg/dL has a CrCl of 65 mL/min.
Which weight should I enter?
The one your drug information or protocol names. The calculator uses whatever weight you type. The original study used actual body weight, but for people with obesity many protocols and product leaflets specify ideal or adjusted body weight. It’s best to follow the guidance for the drug you are checking.
How is creatinine in µmol/L handled?
Select µmol/L as the Creatinine unit and the calculator divides by 88.4 to get mg/dL before applying the equation. If your lab reports mg/dL, select mg/dL and enter the value as it is. Some references write the formula with a factor of 1.23 and creatinine in µmol/L; it is the same equation.
What is the difference between CrCl and eGFR?
CrCl from Cockcroft-Gault is an absolute value in mL/min that depends on body weight. eGFR from CKD-EPI is indexed to 1.73 m² of body surface area. They are different numbers, and a drug label usually names the one it was studied with. Our guide on eGFR versus creatinine clearance compares them.
Why is the female factor 0.85?
To allow for lower creatinine production. Cockcroft and Gault studied men and suggested reducing the result by 15% for women, because women have lower average muscle mass and therefore produce less creatinine. The factor is an estimate, not a measured value, and it applies whatever the woman’s build.
Can I use it in children?
No. Cockcroft-Gault was developed in adults, and the calculator shows a warning for ages under 18. Paediatric kidney function is estimated with different equations that use height rather than weight. For renal dose adjustment in children, we recommend following your local paediatric guidance.