Cockcroft-Gault Formula: How to Calculate Creatinine Clearance (With Examples)

When a medicine is cleared by the kidneys, the safe dose depends on how well those kidneys are working. A blood creatinine level on its own does not tell you that, because the same creatinine can mean very different kidney function in a 25-year-old athlete and an 85-year-old with little muscle. The Cockcroft-Gault formula solves part of this by combining creatinine with age, weight and sex to estimate creatinine clearance (CrCl). This guide explains the formula in both unit systems, shows which body weight to use, gives you quick-reference tables and six worked examples, and explains where the estimate can mislead you.

Table of Contents

1. What creatinine clearance means
2. The Cockcroft-Gault formula
3. Where the formula came from
4. Which weight should you use?
5. Step-by-step calculation
6. How age and creatinine change the answer
7. Six worked examples
8. What the number means for drug dosing
9. Cockcroft-Gault vs eGFR vs 24-hour urine
10. Limitations
11. Common mistakes
12. Tips for students, nurses and pharmacists
13. Frequently asked questions
14. Key takeaways

1. What Creatinine Clearance Means

Creatinine is a waste product made by muscles at a fairly steady rate. The kidneys filter it out of the blood, so when the kidneys slow down, creatinine builds up. Creatinine clearance is the volume of blood plasma the kidneys clear of creatinine each minute, expressed in mL/min. It is a practical stand-in for how well the kidneys filter, and it is the number many drug labels use when they set dose limits.

Measuring it directly means collecting urine for 24 hours, which is slow and often inaccurate. So clinicians estimate it with a formula. Related ideas, like how much urine a patient produces, are covered in our guide to normal urine output.

2. The Cockcroft-Gault Formula

Conventional units (creatinine in mg/dL, weight in kg):

CrCl (mL/min) = [(140 − age) × weight] / (72 × serum creatinine)
× 0.85 if the patient is female

SI units (creatinine in µmol/L):

Men:   CrCl (mL/min) = (140 − age) × weight × 1.23 / serum creatinine
Women: CrCl (mL/min) = (140 − age) × weight × 1.04 / serum creatinine

Converting creatinine: 1 mg/dL = 88.4 µmol/L. The constants 1.23 and 1.04 come from 88.4 ÷ 72, with the female value multiplied by 0.85.

Three things to notice:

• The result is not adjusted for body size, so it is in plain mL/min, unlike eGFR.
• The formula assumes stable kidney function.
• Age lowers the answer because muscle mass and creatinine production fall as we get older.

3. Where the Formula Came From

Donald Cockcroft and Henry Gault published the equation in the journal Nephron in 1976. They built it for adult men by studying how 24-hour creatinine excretion per kilogram changed with age in 249 patients aged 18 to 92, then tested it against measured clearances in 236 patients. The predicted and measured values correlated at 0.83. For women the result is taken as 15% lower. The authors also stressed that factors for age and body weight must be included to get a reasonable prediction.

The original work used older, non-standardized creatinine assays, which is one reason modern eGFR equations were developed. Even so, Cockcroft-Gault remains the standard reference in many drug labels. You can read the original abstract at Prediction of creatinine clearance from serum creatinine.

4. Which Weight Should You Use?

This is the part most students get wrong. Creatinine comes from muscle, not from fat, so using total body weight in an obese patient makes the kidneys look better than they are.

Patient group	Weight commonly used
Underweight (BMI below 18.5)	Actual body weight
Normal weight (BMI 18.5 to 24.9)	Ideal body weight (or actual if it is lower)
Overweight or obese (BMI 25 and above)	Adjusted body weight

The formulas for the weights:

Ideal body weight (Devine):
  Men:   50 kg   + 2.3 kg × (height in inches − 60)
  Women: 45.5 kg + 2.3 kg × (height in inches − 60)

Adjusted body weight = IBW + 0.4 × (actual weight − IBW)

For a deeper explanation of these weights, see our guide to the ideal body weight formulas.

Important: There is no single universal rule. Different hospitals, drug labels and pharmacists choose differently. A common alternative is to calculate with several weights and look at the range. Always follow your local protocol, and see this MDCalc overview of the Cockcroft-Gault equation for more on the weight options.

5. Step-by-Step Calculation

1. Collect the data: age, sex, weight, height (if you need IBW) and serum creatinine.
2. Check the units. Creatinine must be in mg/dL for the first formula, or µmol/L for the SI version.
3. Choose the weight using the table above.
4. Calculate (140 − age) × weight.
5. Divide by 72 × serum creatinine.
6. Multiply by 0.85 if the patient is female.
7. Check that it makes sense for the patient and the clinical picture.

6. How Age and Creatinine Change the Answer

These two original tables use a 75 kg man to show how sensitive the formula is.

Effect of age (serum creatinine 1.0 mg/dL):

Age	CrCl (mL/min)
30	114.6
50	93.8
70	72.9
90	52.1

Effect of creatinine (age 70, weight 75 kg):

Serum creatinine (mg/dL)	CrCl (mL/min)
0.8	91.1
1.0	72.9
1.5	48.6
2.0	36.5
3.0	24.3
4.0	18.2

Since creatinine is in the denominator, doubling the creatinine halves the clearance (as long as the other inputs stay the same and the kidney function is stable). This is why even a modest rise in creatinine can mean a large drop in kidney function.

7. Six Worked Examples

Example 1: Man with typical numbers.
Male, 70 years, 75 kg, creatinine 1.0 mg/dL.
CrCl = (140 − 70) × 75 / (72 × 1.0) = 5,250 / 72 = 72.9 mL/min.

Example 2: Same patient, but female.
Female, 70 years, 75 kg, creatinine 1.0 mg/dL.
CrCl = 72.9 × 0.85 = 62.0 mL/min.

Example 3: Obese patient (which weight?).
Male, 55 years, 100 kg, height 5 ft 10 in, creatinine 1.2 mg/dL. BMI is about 31.6, so he is obese.

Weight used	Weight (kg)	CrCl (mL/min)
Actual	100	98.4
Ideal (73.0 kg)	73.0	71.8
Adjusted (73.0 + 0.4 × 27 = 83.8 kg)	83.8	82.4

Actual weight gives an estimate about 16 mL/min higher than the adjusted weight. Following the common approach for BMI of 25 or more, the adjusted result of about 82 mL/min would be used.

Example 4: Older woman with low weight.
Female, 82 years, 48 kg, creatinine 0.9 mg/dL.
CrCl = (140 − 82) × 48 × 0.85 / (72 × 0.9) = 2,366.4 / 64.8 = 36.5 mL/min.
Her creatinine of 0.9 looks “normal,” yet her clearance is moderately reduced. This is a classic example of why creatinine alone can mislead in older, small patients.

Example 5: SI units.
Male, 65 years, 80 kg, creatinine 106 µmol/L.
CrCl = (140 − 65) × 80 × 1.23 / 106 = 7,380 / 106 = 69.6 mL/min.

Example 6: Using the result for a dosing check.
A drug label says to reduce the dose if CrCl is below 50 mL/min. Example 4 (36.5 mL/min) is below that line, while Example 1 (72.9 mL/min) is above it. The pharmacist or prescriber must then apply the label’s exact instructions.

8. What the Number Means for Drug Dosing

Most drug labels use cut-offs, and common ones are 60, 30 and 15 mL/min. A rough guide to what the number says about filtration:

CrCl (mL/min)	General meaning
Above 90	Normal filtration
60 to 89	Mildly reduced
30 to 59	Moderately reduced
15 to 29	Severely reduced
Below 15	Kidney failure range

Healthy young adults often have values around 90 to 130 mL/min, which then fall with age. Formal CKD staging uses eGFR rather than this table. Medicines whose doses depend on CrCl include many antibiotics, anticoagulants and drugs cleared by the kidneys, so the exact thresholds always come from the drug label or hospital guideline.

9. Cockcroft-Gault vs eGFR vs 24-Hour Urine

Feature	Cockcroft-Gault	eGFR (CKD-EPI)	24-hour urine CrCl
What it gives	Estimated CrCl (mL/min)	Estimated GFR (mL/min/1.73 m²)	Measured CrCl
Uses weight	Yes	No (indexed to body surface area)	No
Best for	Drug dosing when labels cite CrCl	Staging chronic kidney disease	Special situations needing a measurement
Needs a urine collection	No	No	Yes, 24 hours
Main weakness	Weight and muscle mass effects	Not designed for every dosing label	Collection errors

The two estimates can differ noticeably in very obese, very thin or elderly patients, so use the one your guideline asks for.

10. Limitations

• Unstable kidney function. In acute kidney injury, creatinine has not reached a steady state, so the formula does not reflect current function.
• Weight extremes. It is less accurate in obesity, wasting and very low weight.
• Muscle mass. Older adults, amputees, malnourished patients and bodybuilders have creatinine levels that do not reflect the same kidney function.
• Pregnancy. It is not validated in pregnancy.
• Advanced kidney disease. The kidney’s tubules secrete some creatinine, so clearance can be overestimated.
• Old lab methods. The original used non-standardized creatinine measurements.
• Not for CKD staging. Use eGFR for that purpose.

11. Common Mistakes

• Using µmol/L in the mg/dL formula (the answer will be wildly wrong).
• Forgetting the 0.85 factor for women.
• Using actual weight in obese patients without considering the adjusted weight.
• Applying the formula during acute kidney injury.
• Mixing up CrCl and eGFR when reading a drug label.
• Using the wrong units for height when working out IBW (inches in the standard formula).
• Rounding too early in the calculation.

12. Tips for Students, Nurses and Pharmacists

• Memorize the structure as “age and weight on top, creatinine on the bottom.”
• The female factor is 0.85, and the SI constants are 1.23 (men) and 1.04 (women).
• Write down the weight basis you used (actual, ideal or adjusted) next to the result.
• Check creatinine trends, not just one value.
• If creatinine is changing quickly, treat any CrCl estimate as unreliable and ask for clinical review.
• Look at the drug label to see whether it asks for CrCl or eGFR.
• Use our medical tools to practice related calculations.

13. Frequently Asked Questions

What is the Cockcroft-Gault formula?
CrCl = [(140 − age) × weight] / (72 × serum creatinine), multiplied by 0.85 for women, with creatinine in mg/dL and weight in kg.

What is the Cockcroft-Gault formula in µmol/L?
CrCl = (140 − age) × weight × 1.23 / serum creatinine for men, and × 1.04 instead of 1.23 for women.

Which weight should I use in Cockcroft-Gault?
It depends on the protocol, but commonly actual weight when underweight, ideal weight at normal BMI, and adjusted weight when overweight or obese.

What is a normal creatinine clearance?
Roughly 90 to 130 mL/min in healthy younger adults, falling gradually with age.

Why is the result multiplied by 0.85 for women?
Women generally have less muscle mass and make less creatinine, so the original authors reduced the estimate by 15%.

Is Cockcroft-Gault the same as eGFR?
No. Cockcroft-Gault gives CrCl in mL/min using weight, while eGFR is indexed to body surface area and is used for CKD staging.

Why is Cockcroft-Gault used for drug dosing?
Many drug labels were built on clinical studies that used CrCl, and regulators still refer to it for dosing.

Does the formula work in acute kidney injury?
Not reliably, because creatinine is changing and has not reached a steady state.

Can I use Cockcroft-Gault in children?
No. It is meant for adults, and children use other equations.

Why does obesity change the result?
Fat does not make creatinine, so using total weight makes the kidneys look better than they are.

What is adjusted body weight?
Ideal body weight plus 40% of the excess over the ideal weight.

What creatinine units does the formula need?
mg/dL for the standard version, or µmol/L for the SI version. Convert using 1 mg/dL = 88.4 µmol/L.

Cockcroft-Gault Formula Knowledge Quiz

14. Key Takeaways

• Cockcroft-Gault estimates creatinine clearance from age, weight, sex and serum creatinine.
• Formula: [(140 − age) × weight] / (72 × creatinine), × 0.85 for women.
• Weight choice matters: actual, ideal or adjusted, depending on BMI and local protocol.
• Doubling the creatinine roughly halves the clearance when kidney function is stable.
• It is unreliable in acute kidney injury, pregnancy and weight extremes.
• Use it for drug dosing when labels cite CrCl, and use eGFR for CKD staging.

Disclaimer: This article is for educational purposes only and is not a substitute for professional medical advice. Drug doses must be set by a qualified prescriber or pharmacist according to the product label and local guidelines.

References

• Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41.
• MDCalc: Creatinine Clearance (Cockcroft-Gault Equation).
• Kidney Disease: Improving Global Outcomes (KDIGO) guidance on evaluation of chronic kidney disease.