GFR Calculator: Creatinine Clearance (Cockcroft-Gault)
The Cockcroft-Gault equation is the most widely used formula for estimating creatinine clearance (CrCl) and is the standard reference for drug dosing in renal impairment. Developed by Cockcroft and Gault in 1976, it uses serum creatinine, age, body weight, and sex to estimate the rate at which the kidneys clear creatinine from the blood. This is used by pharmacists and physicians to adjust medication doses for patients with reduced kidney function, preventing drug toxicity and ensuring therapeutic efficacy. For CKD staging and clinical classification, the race-free 2021 CKD-EPI eGFR equation is preferred. This calculator is for educational purposes - all clinical drug dosing decisions should involve a pharmacist or physician.
Cockcroft-Gault equation
CrCl (mL/min) = ((140 - Age) x Weight x Sex factor) / (72 x Serum Creatinine mg/dL)
Sex factor: Male = 1.0; Female = 0.85
Drug dosing thresholds: above 60 = normal; 30-60 = moderate; 15-30 = severe; below 15 = failure
GFR and CrCl: frequently asked questions
What is the difference between GFR and eGFR?
True GFR (glomerular filtration rate) measures the volume of plasma filtered by the kidneys per minute and requires inulin or iohexol clearance studies. eGFR (estimated GFR) uses serum creatinine with the CKD-EPI equation to estimate GFR for CKD staging. Creatinine clearance (CrCl) from the Cockcroft-Gault formula estimates GFR for drug dosing - it tends to overestimate slightly compared to eGFR. This calculator computes Cockcroft-Gault CrCl.
When is the Cockcroft-Gault formula used?
The Cockcroft-Gault equation is the standard for drug dosing adjustments in patients with renal impairment. It was developed in 1976 using 24-hour urine creatinine data. Most medication dosing guidelines (FDA, pharmacopoeias) reference Cockcroft-Gault CrCl. The CKD-EPI equation is preferred for CKD staging and prognostic purposes. Both require serum creatinine, age, and body weight.
What is a normal creatinine clearance?
Normal creatinine clearance varies by age and sex: young adult males: 80-125 mL/min/1.73 m2; young adult females: 75-115 mL/min/1.73 m2. Values decline progressively with age (approximately 1 mL/min per year after age 40). Drug dosing thresholds typically reference: above 60 mL/min = normal dosing; 30-60 mL/min = moderate renal impairment (dose adjust); 15-30 mL/min = severe impairment; below 15 mL/min = kidney failure.
How does obesity affect the Cockcroft-Gault result?
The original Cockcroft-Gault formula uses actual body weight (ABW). In obese patients (BMI above 30), this overestimates creatinine clearance because adipose tissue contributes little to creatinine production. Most guidelines recommend using ideal body weight (IBW) for obese patients, with some using adjusted body weight (ABW + 0.4 x excess weight). This calculator lets you enter either actual or ideal body weight depending on your clinical situation.
Should I use Cockcroft-Gault or CKD-EPI?
Use Cockcroft-Gault CrCl for drug dosing decisions - this is what most prescribing information and renal dosing references use. Use the CKD-EPI eGFR for CKD staging, prognosis, and KDIGO classification. The 2021 race-free CKD-EPI equation (see our eGFR calculator) has replaced the 2009 equation as the standard for CKD classification. Cockcroft-Gault remains the standard for pharmacokinetic dosing because it was the equation used in most drug development studies.
Official sources
- National Kidney Foundation: Glomerular Filtration Rate (GFR).
- FDA: Renal Dosing in Drug Labeling.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.