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Cockcroft-Gault Calculator with BMI Adjustment

Estimate Glomerular Filtration Rate (eGFR) for medication dosing. Features automatic Adjusted Body Weight logic for obese patients to prevent overdosing.

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About

The Cockcroft-Gault equation remains the industry standard for adjusting drug dosages (such as antibiotics and DOACs) based on renal function. Unlike newer equations like MDRD or CKD-EPI, Cockcroft-Gault relies heavily on patient weight. This introduces a significant safety risk: using the total body weight of an obese patient can vastly overestimate clearance, leading to toxic drug levels.

This calculator integrates "Safety-First" logic. It automatically calculates Ideal Body Weight (IBW) and Body Mass Index (BMI). If the patient is significantly obese (BMI > 30), the tool alerts the user and defaults to the Adjusted Body Weight (AdjBW) method, following clinical best practices.

pharmacy drug dosing creatinine clearance IBW medical

Formulas

The primary formula calculates creatinine clearance (CrCl) in mL/min. The weight (Wt) used depends on the BMI classification.

CrCl = (140 − age) × Weightkg72 × SCr × (0.85 if female)

Logic used for Weight Selection:

  • If TBW < IBW: Use TBW (Total Body Weight)
  • If TBW > 120% of IBW: Use AdjBW (Adjusted Body Weight)
  • Otherwise: Use IBW or TBW based on institutional protocol (This tool uses IBW).

Reference Data

VariableMale FormulaFemale Formula
Ideal Body Weight (IBW)50 + 2.3 × (Htin − 60)45.5 + 2.3 × (Htin − 60)
Adjusted Weight (AdjBW)IBW + 0.4 × (TBW − IBW)
Cockcroft-Gault(140 − Age) × Wt72 × SCrMale × 0.85

Frequently Asked Questions

While CKD-EPI is more accurate for staging kidney disease, most FDA-approved drug package inserts explicitly base dosing adjustments on the Cockcroft-Gault equation. Using a different formula could lead to incorrect legal dosing.
Creatinine is a byproduct of muscle metabolism. Adipose tissue (fat) produces very little creatinine. In obese patients, using total weight assumes they have massive muscles, leading to a dangerously high calculated clearance. Adjusted Body Weight corrects for this by adding only a fraction (40%) of the excess weight.
Some institutions round serum creatinine up to 0.8 or 1.0 for elderly patients with low muscle mass to avoid overestimating function. This tool uses the raw input value. You should manually round up the input if your clinical protocol requires it.