How to Calculate Creatinine Clearance (Cockcroft–Gault)

What Cockcroft–Gault is for

Cockcroft–Gault remains the reference equation for renal dose adjustment because the pharmacokinetic studies underpinning FDA labelling used it. It is not the same as an eGFR reported by the laboratory, which uses CKD-EPI and is normalised to 1.73 m². When a package insert specifies a creatinine clearance threshold, it means this equation.

The formula

CrCl (mL/min) = [(140 − age) ÷ (72 × SCr)] × weight × (0.85 if female)

Age is in years, serum creatinine (SCr) in mg/dL, and weight in kg. The 0.85 factor for female sex reflects lower average muscle mass in the original cohort, not a physiological correction applied to every equation of this kind.

Step by step

Enter age, sex, and serum creatinine. The creatinine unit dropdown converts µmol/L automatically.
Enter total body weight. Add a height if you want the ideal or adjusted body weight options.
Choose which weight the equation should use, then compare the three CrCl values shown in the result panel to see how much the choice matters for this patient.

Worked example

A 72-year-old female is 160 cm and weighs 65 kg, with a serum creatinine of 1.4 mg/dL. Estimate her creatinine clearance for renal dose adjustment.

Answer: [(140 − 72) ÷ (72 × 1.4)] × 65 × 0.85 = (68 ÷ 100.8) × 65 × 0.85 = 37.3 mL/min — moderate impairment, so most renally cleared drugs will need adjustment. The height is supplied so the result panel can also show what the estimate would be using ideal and adjusted body weight.

What the result does and does not mean

Cockcroft–Gault estimates creatinine clearance in mL/min. A laboratory-reported eGFR is a different quantity, uses a different equation, and is normalised to 1.73 m² of body surface area. Do not substitute one for the other when a package insert specifies a CrCl threshold.
The equation assumes steady-state renal function. In acute kidney injury the creatinine lags behind the true clearance, so a rising creatinine means the real clearance is already lower than calculated — and a falling creatinine means it is higher.
Creatinine is generated by muscle. Low muscle mass — advanced age, amputation, spinal cord injury, cachexia, cirrhosis — produces a low creatinine that overstates renal function.

When the estimate should not be trusted

Derived in 1976 from 249 hospitalised men. Female patients are represented only by an applied 0.85 factor, not by independent derivation.
Invalid in unstable or rapidly changing renal function, including acute kidney injury and the immediate post-dialysis period.
Unreliable at the extremes of body habitus. In obesity, total body weight substantially overestimates clearance; the choice of weight can change the answer by a factor of two.
Not validated in children, in pregnancy, or in patients on renal replacement therapy.
Estimates creatinine clearance, which itself overestimates true glomerular filtration rate because creatinine is secreted as well as filtered.

Practical adjustments that change the answer

Rounding a low serum creatinine up to 1.0 in older adults is a widespread institutional practice with no prospective validation. It systematically underestimates clearance and can lead to underdosing. Know whether your institution does it, and be consistent.
Drugs that alter creatinine secretion without changing GFR — trimethoprim, cimetidine, cobicistat, dolutegravir — raise the measured creatinine and make the estimate falsely low.

References

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41.
US Food and Drug Administration. Guidance for Industry: Pharmacokinetics in Patients with Impaired Renal Function — Study Design, Data Analysis, and Impact on Dosing. link
Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314.
Winter MA, et al. Impact of various body weights and serum creatinine concentrations on the bias and accuracy of the Cockcroft-Gault equation. Pharmacotherapy. 2012;32(7):604-612.