Free renal tool
Creatinine clearance calculator
Estimate creatinine clearance with the Cockcroft-Gault equation from age, sex, weight, and serum creatinine — the check nurses make before many renally-cleared medications — and see the full worked setup behind the number. This estimates CrCl, which approximates but is not an exact measured GFR. Free, no signup.
Interactive calculator
Creatinine clearance calculator
Enter age, sex, weight, and serum creatinine to estimate creatinine clearance with the Cockcroft-Gault equation, and see the worked setup below. This estimates CrCl, which approximates GFR but is not an exact measured GFR. Results update as you type.
Result
Enter age, sex, weight, and serum creatinine to see the estimate and the worked setup.
For education and practice only. Cockcroft-Gault estimates creatinine clearance, not an exact GFR; always independently verify a renal dosing decision before acting on it.
How it works
The Cockcroft-Gault equation
Published by Cockcroft and Gault in 1976, this equation estimates creatinine clearance from four bedside variables. It is still widely used for renal drug-dose adjustments.
Creatinine clearance (mL/min)
CrCl = [(140 − age) × weight kg × (0.85 if female)] ÷ (72 × SCr)
Age is in years, weight in kilograms, and serum creatinine (SCr) in mg/dL. Multiply the numerator by 0.85 for females to adjust for lower average muscle mass.
Pounds to kilograms
kg = lb ÷ 2.2
The equation needs weight in kilograms. If the weight is recorded in pounds, divide by 2.2 first — this calculator does the conversion and shows it in the worked steps.
Worked example
A Cockcroft-Gault estimate, step by step
The patient
A 60-year-old male weighing 80 kg with a serum creatinine of 1.0 mg/dL. What is the estimated creatinine clearance?
The setup
- 1. Numerator: (140 − 60) × 80 = 80 × 80 = 6,400.
- 2. Male, so no 0.85 factor.
- 3. Denominator: 72 × 1.0 = 72.
- 4. CrCl = 6,400 ÷ 72 = 88.9 mL/min.
Answer: ≈ 88.9 mL/min.
Reading the result
An estimate near 89 mL/min is a mildly-reduced-to-normal clearance. If this same patient were female, multiplying the numerator by 0.85 would give 6,400 × 0.85 ÷ 72 ≈ 75.6 mL/min.
Enter these numbers in the calculator above to see the identical worked setup returned. Remember this is an estimate of creatinine clearance, not a measured GFR.
Because serum creatinine sits in the denominator, small lab changes move the estimate a lot — a reason it is unreliable in acute kidney injury before creatinine reaches steady state.
Common questions
Creatinine clearance, explained
CrCl (mL/min) = [(140 − age) × weight in kg × (0.85 if female)] ÷ (72 × serum creatinine in mg/dL). Convert the weight to kilograms first if it is in pounds (lb ÷ 2.2), multiply the numerator, then divide by 72 times the serum creatinine.
No. The Cockcroft-Gault equation estimates creatinine clearance (CrCl), which approximates the glomerular filtration rate but is not an exact measured GFR. CrCl tends to slightly overestimate true GFR because a small amount of creatinine is secreted by the tubules. Many drug references still use Cockcroft-Gault CrCl for renal dose adjustments, so it remains widely calculated.
The 0.85 factor adjusts for the lower average muscle mass, and therefore lower creatinine production, in females. It is applied to the whole numerator, reducing the estimated clearance by 15% compared with the same numbers in a male.
The original equation uses actual body weight, and that is what this calculator uses. In practice, some clinicians use ideal or adjusted body weight for patients who are underweight, obese, or edematous. Follow your institution's pharmacy guidance for those situations; this tool is for study and estimation.
It is least reliable at extremes of body weight, in acute kidney injury (where serum creatinine is changing and has not reached steady state), in the very elderly, and in people with very low muscle mass. In those settings a measured clearance or a specialist assessment is more appropriate.
Yes. It is completely free, needs no account, and runs entirely in your browser, so it works on a phone. It is a study and practice aid only — always verify a real renal-dosing decision against the drug reference, pharmacy, and institutional policy.
Connect the math to the pharmacology
Study renal dosing, then practice it
Estimating clearance is only useful if you know which drugs need adjusting. Review the pharmacology study guide, drill pharmacology and med-surg questions, or explore the other free calculators.
This calculator and all study material on this site are provided for practice and study only. Cockcroft-Gault estimates creatinine clearance, not an exact GFR. Verify every renal-dosing decision before acting on it.
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Apply it on real NCLEX-style questions
A calculator hands you the number; the exam makes you reach it under pressure and defend it. Drill Pharmacology questions that put this calculation inside a realistic clinical scenario — each one with a written rationale, so you learn why the answer is right, not just what it is. That explained-rationale practice is what sets us apart from a bare calculator.
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