Cockcroft-Gault Creatinine Clearance Calculator
Cockcroft-Gault creatinine clearance calculator. Estimate CrCl from age, weight, serum creatinine and sex for renal drug-dosing checks. Educational only.
Cockcroft-Gault Creatinine Clearance Calculator
Please tick the acknowledgement above before calculating.
How to use the Cockcroft-Gault calculator
Pick your creatinine units
Use mg/dL (US convention) or µmol/L (SI, most of the world). The calculator converts SI to mg/dL internally by dividing by 88.4, so the equation is applied consistently.
Enter age, weight and creatinine
Use the patient's actual body weight in kilograms and a recent, stable serum creatinine. In obesity, ideal or adjusted body weight is usually substituted — see the note below the result.
Select sex
Female sex multiplies the result by 0.85 to reflect lower average muscle mass and therefore lower creatinine generation.
Acknowledge, then read the band
Tick the acknowledgement to reveal the estimate. Cockcroft-Gault is the equation most drug labels use for renal dose adjustment — note the common cutoffs (≈50, 30, 15 mL/min) shown with the result, and confirm against your institution's drug-information reference.
Cockcroft-Gault and why it still runs drug dosing
An estimate built for the pharmacy, not the clinic wall
The Cockcroft-Gault equation, published in 1976, estimates creatinine clearance (CrCl) — a stand-in for how fast the kidneys filter blood — from four everyday variables: age, body weight, serum creatinine, and sex. Its logic is simple. Creatinine is a muscle by-product produced at a fairly steady rate and cleared almost entirely by the kidneys, so the blood level rises as kidney function falls. Younger, heavier people generate more creatinine, so the numerator scales with (140 − age) × weight; women generate less per kilogram, hence the 0.85 factor; and the denominator divides by serum creatinine because a higher level means worse clearance. The result is an unnormalised clearance in millilitres per minute — a whole-body number, not a body-surface-area-indexed one. That distinction is the whole reason the equation survives in an age of newer formulas: most drug manufacturers ran their renal-dosing studies using Cockcroft-Gault, so the dose-adjustment thresholds printed on drug labels are anchored to this estimate, not to eGFR.
For staging chronic kidney disease, the modern preference is the CKD-EPI 2021 eGFR equation, which is indexed to 1.73 m² and better calibrated across populations. But for deciding whether to reduce a dose of a renally cleared drug — many antibiotics, anticoagulants, antivirals and chemotherapeutics — Cockcroft-Gault remains the reference because it matches the data the dosing recommendations were derived from. The two answers can differ, especially at the extremes of body size, which is exactly why the equation you use matters.
"Cockcroft-Gault isn't the best estimate of kidney function — it's the one the drug labels were written against. That's why pharmacists still reach for it before adjusting a renally cleared dose."
Where it goes wrong — and the body-weight trap
Because the equation multiplies by actual body weight, it overestimates clearance in obese patients (extra fat adds weight but not creatinine-generating muscle) and can mislead in oedema, amputation, or rapidly changing renal function, where a single creatinine no longer reflects a steady state. The usual fixes are to substitute ideal body weight, or an adjusted body weight when the patient is well above ideal, and to avoid the equation entirely when creatinine is moving day to day (acute kidney injury). It also loses accuracy at the extremes of age and in very low muscle mass, where a "normal" creatinine can hide significant impairment. None of this makes the estimate useless — it makes it an estimate, to be read with its assumptions in mind and confirmed against local dosing guidance. Used that way, across any healthcare system from a Singapore tertiary hospital to a rural clinic, it remains one of the most consequential back-of-envelope calculations in medicine.
10 Facts About Cockcroft-Gault
Published in 1976 by Cockcroft and Gault.
CrCl = (140 − age) × weight × (0.85 if female) / (72 × SCr mg/dL).
It estimates an unnormalised clearance in mL/min — not per 1.73 m².
Drug labels base renal dose adjustments on this equation.
Common dose cutoffs sit near 50, 30 and 15 mL/min.
It overestimates clearance in obesity (use adjusted weight).
SI creatinine in µmol/L ÷ 88.4 = mg/dL.
Not valid in acute kidney injury — creatinine isn't at steady state.
CKD-EPI 2021 eGFR is preferred for staging CKD.
Low muscle mass can mask impairment behind a normal creatinine.
Frequently asked questions
CrCl (mL/min) = [(140 − age) × weight in kg × (0.85 if female)] ÷ [72 × serum creatinine in mg/dL]. It estimates creatinine clearance, a proxy for kidney filtration, from four routine variables. If your creatinine is in µmol/L, divide it by 88.4 first to convert to mg/dL.
For staging chronic kidney disease, eGFR (CKD-EPI 2021) is preferred. But most drug manufacturers ran their renal dose-adjustment studies using Cockcroft-Gault, so the cutoffs printed on drug labels refer to this estimate. Pharmacists therefore use Cockcroft-Gault to decide whether to reduce the dose of a renally cleared drug. The two can disagree, especially at the extremes of body size.
For normal-weight adults, actual body weight is used. Because the equation scales with weight, it overestimates clearance in obesity, so ideal body weight (or an adjusted body weight partway between ideal and actual) is commonly substituted when a patient is well above their ideal weight. In underweight patients, actual weight is usually appropriate. Follow your local pharmacy guidance for the exact weight descriptor.
Women on average have lower muscle mass than men of the same weight, and muscle is the source of creatinine. Less creatinine is generated per kilogram, so the original equation applies a 0.85 multiplier for female sex to avoid overestimating clearance. It is an average correction, not an individual measurement.
No. Cockcroft-Gault assumes a stable, steady-state creatinine. In acute kidney injury the creatinine is rising or falling and lags behind the true clearance, so the estimate can be very misleading. When renal function is changing day to day, clinicians rely on the trend, urine output, and clinical judgement rather than a single computed clearance.
Many drug labels specify a reduced dose, extended interval, or avoidance below certain CrCl thresholds — commonly around 50, 30, and 15 mL/min, though the exact numbers vary by drug. The calculator flags which band your estimate falls into so you know to check the specific drug's renal-dosing section. Always confirm the precise cutoff for the actual medication in your institution's drug-information reference.
It is a population estimate, typically within about 20% of measured clearance in stable adults of average build. Accuracy falls in obesity, very low muscle mass, the very elderly, oedema, and unstable renal function. It also doesn't account for diet (e.g., recent large meat intake) or muscle-wasting illness. Treat the number as a guide that informs a decision, not a measured value.
No. This tool is educational. Renal dose adjustment is a clinical decision that depends on the specific drug, the indication, other organ function, interacting medications, and the trend in kidney function. Never start, stop, or change a dose based on a calculator. Use it to understand the concept and to have an informed conversation with your doctor or pharmacist.
Yes. Switch the units toggle to µmol/L and enter your creatinine in SI units; the calculator divides by 88.4 to convert to mg/dL before applying the equation. Weight is always in kilograms. This makes the tool usable across the US (mg/dL) and most other countries (µmol/L) without manual conversion.
No. Age, weight, creatinine and sex are processed entirely in your browser — nothing is sent to a server, stored, or shared. No protected health information leaves your device. You can use the tool without an account and close the page knowing nothing was recorded.
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