Cockcroft-Gault Equation: The Creatinine Clearance Formula

The Cockcroft-Gault equation is the standard formula for estimating creatinine clearance (CrCl) in mL/min from age, weight, sex, and serum creatinine. Donald Cockcroft and Henry Gault published it in the journal Nephron in 1976, and it has been used for almost 50 years to guide medication dosing in people with reduced kidney function.

The Creatinine Clearance Formula

CrCl (mL/min) = [(140 − age) × weight in kg] ÷ (72 × serum creatinine in mg/dL)

For women, multiply the result by 0.85.

Age is entered in years, weight in kilograms, and serum creatinine in mg/dL. The answer is an absolute clearance in mL/min, not the mL/min/1.73 m² used for eGFR, so it can be matched directly to the creatinine clearance cut-offs printed in drug labels.

Worked Example: Step by Step

Take a 70-year-old man weighing 80 kg with a serum creatinine of 1.2 mg/dL:

1. Age term: 140 − 70 = 70.
2. Numerator: 70 × 80 kg = 5,600.
3. Denominator: 72 × 1.2 mg/dL = 86.4.
4. Divide: 5,600 ÷ 86.4 = 64.8, a creatinine clearance of about 65 mL/min.
5. For an otherwise identical woman: 64.8 × 0.85 = 55.1, or about 55 mL/min once the estimate is scaled for lower average muscle mass.

To skip the arithmetic, enter the same values in the creatinine clearance calculator, which also converts µmol/L and applies the body-weight rule described below.

The Four Inputs

The Cockcroft-Gault equation needs only four routinely available variables. Each one moves the result in a defined direction, so the formula is transparent enough to compute by hand.

The numerator multiplies the age term by body weight, which scales the estimate to muscle mass: larger patients generate and clear more creatinine. The denominator, 72 × serum creatinine, carries the marker the kidneys must remove. Choose the right body weight: actual weight when it is below ideal, ideal body weight from ideal up to 130% of ideal, and adjusted body weight above 130% of ideal. Convert units with the creatinine unit converter first if your lab reports serum creatinine in µmol/L (divide by 88.4 to reach mg/dL).

The 0.85 Female Factor

The 0.85 multiplier for female patients adjusts for lower average muscle mass, and therefore lower creatinine production, at any given serum creatinine. Without it, the equation would systematically overestimate clearance in women.

History and Derivation

Cockcroft and Gault derived the formula from 249 hospitalized men, regressing measured 24-hour creatinine clearance against age, weight, and serum creatinine. The female factor was added by analogy to account for body composition. Because it predicts a timed clearance rather than a body-surface-area-indexed rate, the output is an absolute value in mL/min: the unit drug-dosing studies have used ever since. Henry Gault is the historical co-author and namesake of the equation, not a present-day reviewer of this site. The formula has stayed in use for nearly five decades because it is simple, transparent, and tied to the dosing literature.

Names, Abbreviations, and Units

The Cockcroft-Gault result is most often abbreviated CrCl, short for creatinine clearance. ClCr and CLcr are the same quantity written in pharmacology style, where CL stands for clearance. An "e" prefix, as in eCrCl or the FDA's eCLcr, marks a value estimated from an equation rather than measured from a timed urine collection, and labels and papers also write simply "estimated CrCl". All of these names describe the same Cockcroft-Gault output, and all are reported in mL/min, not in the mL/min/1.73 m² used for eGFR. If your laboratory reports serum creatinine in µmol/L, convert serum creatinine units to mg/dL before entering it.

Choosing the Right Weight

Weight is the input most likely to change the answer, and the right choice depends on how actual weight compares with ideal body weight (IBW). IBW comes from the Devine formula: 50 kg plus 2.3 kg per inch over 5 feet for men, and 45.5 kg plus 2.3 kg per inch over 5 feet for women. The rule used on this site is:

For example, a man who is 5 ft 10 in has an IBW of 50 + (2.3 × 10) = 73 kg, so 130% of IBW is 94.9 kg. At an actual weight of 85 kg, enter 73 kg. At 110 kg, enter adjusted body weight: 73 + 0.4 × (110 − 73) = 87.8 kg.

The rule follows Winter and colleagues (2012), who compared Cockcroft-Gault estimates with measured 24-hour creatinine clearance in 3,678 patients. Actual body weight gave an unbiased estimate in underweight patients, and ideal body weight gave an unbiased estimate in patients of normal weight. In overweight, obese, and morbidly obese patients, adjusted body weight with a 0.4 factor was the least biased and most accurate choice. The FDA 2024 renal impairment guidance makes the same point: in overweight or obese people, ideal or adjusted body weight in Cockcroft-Gault is likely to estimate kidney function more accurately than actual body weight. Some hospitals switch to adjusted body weight at 120% of IBW rather than 130%, and a trial protocol or drug label that sets its own weight rule takes priority over both. The adjusted body weight calculator produces the figure to plug in. For markedly obese patients, the purpose-built Salazar-Corcoran equation is an alternative that uses height and weight together.

How to Read the Result

The Cockcroft-Gault result is a creatinine clearance in mL/min, and it is read against a drug's dosing thresholds. Many labels define cutoffs such as 50, 30, or 15 mL/min that trigger a dose reduction or a switch to an alternative agent. A value of about 65 mL/min reflects mild reduction; one near 30 mL/min often means a meaningful dose change; below 15 mL/min usually signals severe impairment. Always pair the number with the specific drug's renal dosing guidance rather than acting on the figure alone.

Why It Is Still Used for Dosing

Many drug labels set their kidney dose thresholds on Cockcroft-Gault creatinine clearance, because the pharmacokinetic studies behind them estimated kidney function that way. In a review of anticancer drugs approved from 2015 to 2019, estimated creatinine clearance was used in over 60% of pivotal trials and over 80% of renal pharmacokinetic analyses. A label threshold such as "reduce the dose if CrCl < 30 mL/min" therefore maps to a Cockcroft-Gault value, not to an eGFR. Using a different equation can shift a patient across the threshold and change the recommended dose. That is why the equation remains in daily use for renal drug dosing, even though CKD-EPI 2021 is preferred for CKD staging.

Guidance for newer drugs is changing. The FDA's final guidance on pharmacokinetics in renal impairment, issued in March 2024, recommends eGFR over estimated creatinine clearance for assessing kidney function in these studies, because eGFR is so widely available in clinical practice. It still lists Cockcroft-Gault estimated creatinine clearance as an accepted method, and it considers measured GFR, measured creatinine clearance, or any contemporary, widely accepted estimating equation reasonable. Its kidney function bands are 90 mL/min or more for normal function, 60 to under 90 for mild, 30 to under 60 for moderate, and under 30 for severe impairment. The FDA renal impairment categories page explains each band.

The National Kidney Foundation goes further. It advocates moving away from Cockcroft-Gault toward race-free eGFR equations, adjusted to the patient's body surface area, for medication decisions in adults. One reason is creatinine standardisation: by 2011 most serum creatinine assays had been standardised to isotope dilution mass spectrometry (IDMS), and the average serum creatinine value fell by 12%. Because creatinine sits in the denominator, Cockcroft-Gault values calculated today are higher than the values produced in the pharmacokinetic studies used to set dosing recommendations before 2011. NKF also notes that the equation was developed in 249 white men, with the 15% reduction for women estimated rather than measured, and that body weight choices are applied inconsistently between clinicians and institutions. In practice, use the method the drug label or protocol names. See CrCl vs eGFR for the full comparison.

Protocol and Hospital Variants

The core Cockcroft-Gault equation is fixed, while hospitals, trial protocols, and drug labels add their own limits in three places. A weight cap limits how much body weight can enter the equation, a creatinine floor replaces a very low serum creatinine with a minimum value, and a CrCl cap limits the result used for dosing. SWOG Policy 38 is a published example. It uses Cockcroft-Gault with body weight capped at 140% of ideal body weight, a minimum serum creatinine of 0.7 mg/dL, and a maximum creatinine clearance of 125 mL/min for drug dosing.

Institutional rules differ. Some hospitals switch to adjusted body weight at 120% of ideal body weight and others at 130%, and the practice of rounding low creatinine values upward varies widely. The evidence does not support rounding: Winter and colleagues found that rounding a low serum creatinine up to 0.8 or 1.0 mg/dL did not improve the accuracy or bias of the estimate. NKF also points to clear evidence against this empiric adjustment. When a protocol or label sets its own rule, apply that rule and record which one you used. For how these rules are applied when screening patients for studies, see CrCl for clinical trial eligibility.

Strengths and Limitations

The Cockcroft-Gault equation's strengths are simplicity, decades of dosing validation, and an absolute unit that matches drug labels. Its limitations are that it assumes a steady state, depends heavily on the weight chosen, and inherits any error in the serum creatinine measurement. It performs least well at the extremes of body size and in patients with unusual muscle mass, where creatinine generation departs from the population average.