Creatinine clearance calculator (Cockcroft-Gault)
Creatinine Clearance (Cockcroft-Gault) estimates how fast your kidneys clear creatinine from blood, a proxy for kidney function reported in mL/min. Published in 1976, it remains the reference equation clinicians and pharmacists use to adjust drug doses — especially antibiotics, anticoagulants, and renally cleared medications — because most FDA drug labels base renal dosing thresholds on Cockcroft-Gault CrCl rather than eGFR.
How it works
The equation takes age (declining kidney function), body weight (a stand-in for muscle mass, the source of creatinine), and serum creatinine (what's left in blood), then applies a 0.85 factor for females to reflect lower average muscle mass. The exact formula is: CrCl (mL/min) = ((140 − age in years) × weight in kg × [0.85 if female, else 1]) / (72 × serum creatinine in mg/dL). A lower result means slower clearance and poorer kidney function.
Worked example
Take a 65-year-old woman weighing 70 kg with a serum creatinine of 1.1 mg/dL. Numerator: (140 − 65) × 70 × 0.85 = 75 × 70 × 0.85 = 4,462.5. Denominator: 72 × 1.1 = 79.2. CrCl = 4,462.5 / 79.2 ≈ 56 mL/min. For the same person as a male (no 0.85 factor): 75 × 70 / 79.2 ≈ 66 mL/min. A CrCl near 56 mL/min would trigger dose review for many renally cleared drugs.
Important
This is an estimate only and not a substitute for professional medical judgment or a laboratory-reported eGFR. Cockcroft-Gault was derived and validated in adults — do not use it for anyone under 18. It assumes stable kidney function and is unreliable during acute kidney injury, rapidly changing creatinine, pregnancy, extremes of body weight, amputation, or very low muscle mass (elderly, malnourished, spinal cord injury), where it can substantially misestimate clearance. Using actual body weight can overestimate clearance in obesity; clinicians often substitute ideal or adjusted body weight. Results also vary with the lab's creatinine assay (IDMS-standardized methods can shift the number). This estimates creatinine clearance (Cockcroft-Gault), which is not identical to a CKD-EPI eGFR; most FDA renal-dosing thresholds are anchored to Cockcroft-Gault CrCl, so use the measure the drug label specifies. Never start, stop, or change any medication or dose based on this number. Always confirm renal dosing with your physician or pharmacist against the drug's FDA label.