Creatinine clearance calculator (Cockcroft-Gault)

Creatinine clearance by Cockcroft-Gault is [(140 minus age) times weight in kg] divided by (72 times serum creatinine in mg/dL), then multiplied by 0.85 for women. If your laboratory reports creatinine in micromol/L, as most do outside the United States, switch the unit above rather than converting by hand.

When to use the creatinine clearance calculator

Cockcroft-Gault remains the equation most drug labels were written against, so it is what renal dose adjustments are usually based on even where a laboratory reports eGFR instead. Use it when deciding whether a dose needs reducing, not to stage chronic kidney disease.

The creatinine clearance formula

CrCl = [(140 − age) × weight in kg] ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for females.

Worked example

A 65-year-old woman weighs 70 kg with a serum creatinine of 1.0 mg/dL. CrCl = [(140 − 65) × 70] ÷ (72 × 1.0) = 5250 ÷ 72 = 72.9, then × 0.85 = 62 mL/min.

The mistake that costs marks

eGFR and creatinine clearance are not interchangeable. eGFR is normalised to body surface area and reported in mL/min/1.73m², while Cockcroft-Gault gives an absolute value in mL/min. Substituting one for the other misclassifies patients at the extremes of body size, which is exactly where dose adjustment matters most.

Study aid, not a clinical tool

This calculator exists so you can learn the method and check your working for an examination. It is not medical advice and not clinical decision support, and it must not be used to make a decision about a real patient. Verify any result against your local formulary, the product literature and a qualified pharmacist. Our medical disclaimer sets out the full position.

Calculators you will usually need alongside this

Most questions that reach for one of these reach for another a step later, so these are the three that most often pair with it.

• Ideal and adjusted body weight calculator — Ideal body weight
• Body surface area calculator (Mosteller and Du Bois) — Body surface area
• Loading dose calculator — Loading dose

Keep going

Calculations are only half of what examinations test. The other half is knowing why a drug does what it does, which is what decides whether a number you calculated is even the right number to be calculating. Start with Why NSAIDs harm the kidneys. The drug class pages cover the mechanism behind the number, or browse the rest of the free calculators and try the practice questions.