Creatinine Clearance Calculator
Estimate kidney function as creatinine clearance (CrCl) in mL/min using the Cockcroft-Gault equation. Used by clinicians and pharmacists to adjust drug doses in patients with renal impairment.
About this calculator
Creatinine Clearance (CrCl) estimates the glomerular filtration rate (GFR) by measuring how efficiently the kidneys clear creatinine — a metabolic waste product of muscle activity — from the blood. The Cockcroft-Gault equation is: CrCl (mL/min) = [(140 − age) × weight (kg)] / [72 × serum creatinine (mg/dL)], multiplied by 0.85 for females to account for lower average muscle mass. Serum creatinine is measured in mg/dL from a standard blood test. A normal CrCl is approximately 90–120 mL/min; values below 60 indicate chronic kidney disease (CKD), and below 15 indicate kidney failure. Pharmacists routinely use CrCl to adjust doses of renally cleared drugs such as aminoglycosides, digoxin, and direct oral anticoagulants, making this one of the most clinically used equations in medicine.
How to use
Example: a 65-year-old male weighing 75 kg with a serum creatinine of 1.2 mg/dL. Step 1 — Subtract age from 140: 140 − 65 = 75. Step 2 — Multiply by weight: 75 × 75 = 5,625. Step 3 — Multiply denominator: 72 × 1.2 = 86.4. Step 4 — Divide: 5,625 ÷ 86.4 ≈ 65.1 mL/min. No female correction needed (male). A CrCl of 65 mL/min falls in the CKD Stage 2 range, signalling mildly reduced kidney function and the need for dose adjustment for some drugs.
Frequently asked questions
What is the difference between creatinine clearance and GFR, and which should I use?
Creatinine clearance estimated by the Cockcroft-Gault equation and eGFR estimated by the CKD-EPI or MDRD equations are both proxies for glomerular filtration rate but use different mathematical approaches and were validated in different populations. CrCl from Cockcroft-Gault tends to slightly overestimate true GFR because tubular secretion contributes a small amount to creatinine elimination beyond filtration. CKD-EPI eGFR is now preferred for staging chronic kidney disease and cardiovascular risk stratification. However, Cockcroft-Gault remains the standard for drug dosing decisions because most renal dosing studies used this equation to define their dose-adjustment thresholds.
Why is a correction factor of 0.85 applied for females in the Cockcroft-Gault equation?
Creatinine is produced by the breakdown of phosphocreatine in muscle tissue, and women on average have approximately 15% less skeletal muscle mass than men of the same age and weight. Less muscle means less creatinine production, so a given serum creatinine level in a woman corresponds to a higher true GFR than the same level in a man. The 0.85 multiplier was empirically derived to correct for this systematic difference. It is a population-level approximation; highly muscular women or sarcopenic men may not be well represented by this fixed factor.
How does age affect creatinine clearance, and what does a declining CrCl mean for medication safety?
Kidney function declines naturally with age: GFR falls by roughly 1 mL/min/year after the age of 40 due to loss of nephrons, reduced renal blood flow, and structural changes in the glomeruli. The (140 − age) term in the Cockcroft-Gault equation directly encodes this decline. For an elderly patient, even a 'normal' serum creatinine can mask significantly reduced clearance, particularly in those with low muscle mass. Clinically, declining CrCl means renally cleared drugs accumulate to toxic levels faster, so dose reductions or extended dosing intervals are required — a critical consideration for drugs like metformin, dabigatran, and lithium.