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For obese patients, some guidelines recommend using adjusted body weight (ABW) instead of actual body weight.
Renal function staging (CrCl)
| CrCl (mL/min) | Category | Typical drug dosing note |
|---|---|---|
| ≥ 90 | Normal | Standard dosing |
| 60–89 | Mild impairment | Usually standard dosing; check individual drugs |
| 30–59 | Moderate impairment | Many drugs require dose adjustment |
| 15–29 | Severe impairment | Most drugs require dose adjustment or avoidance |
| < 15 | Kidney failure | Dose per dialysis protocol; many drugs contraindicated |
What is creatinine clearance?
Creatinine clearance (CrCl) estimates how much blood plasma the kidneys can clear of creatinine per minute. It is not the same as estimated GFR (eGFR) — CrCl is the standard used in most drug dosing labels and regulatory submissions. The Cockcroft-Gault equation, published in 1976, remains the most widely used formula in clinical pharmacology for adjusting drug doses in renal impairment.
The Cockcroft-Gault formula
CrCl (mL/min) = [(140 − Age) × Weight(kg) × (0.85 if female)] / (72 × Scr in mg/dL)
Where Scr is serum creatinine. For µmol/L, use the modified form: CrCl = [(140 − Age) × Weight × (1.23 if male, 1.04 if female)] / Scr(µmol/L).
Which weight to use
The Cockcroft-Gault equation was originally developed using actual body weight. However, for patients at extremes of body weight, guidelines differ:
- Actual body weight (ABW) — use when body weight is within 20% of ideal.
- Ideal body weight (IBW) — some guidelines recommend IBW for CrCl estimation in obese patients.
- Adjusted body weight (ABW) — recommended by many antimicrobial dosing guidelines for obese patients.
How to use this calculator
- Enter patient age in years (18 or older).
- Enter body weight in kilograms. For obese patients, consider adjusted or ideal body weight.
- Select patient sex.
- Enter serum creatinine and select the unit (mg/dL or µmol/L).
- Click "Calculate creatinine clearance" to see the CrCl value and renal impairment category.
Frequently asked questions
When should I use CrCl vs eGFR?
Use CrCl (Cockcroft-Gault) for drug dosing — most FDA-approved drug labels are based on it. Use eGFR (CKD-EPI) for diagnosing and staging chronic kidney disease. They are not interchangeable.
Is Cockcroft-Gault accurate?
It is the most widely used formula in drug dosing, but it has limitations. It overestimates CrCl in obese patients (uses actual weight), underestimates in elderly patients with low muscle mass, and is not validated in acute kidney injury where creatinine is changing rapidly.
How do I convert mg/dL to µmol/L?
1 mg/dL = 88.42 µmol/L. This calculator handles the conversion automatically when you select the unit.
What does the result mean for drug dosing?
CrCl ≥ 90 mL/min: standard dosing for most drugs. 60–89: usually standard, but check individual drugs. 30–59: many drugs need dose adjustment. 15–29: most drugs need adjustment or should be avoided. < 15: dose per dialysis protocols; many drugs are contraindicated.
Why does the equation use 0.85 for females?
The 0.85 factor accounts for the lower average muscle mass in women, which produces lower baseline serum creatinine at the same kidney function. Without this adjustment, CrCl would be overestimated in female patients.