Creatinine Clearance Calculator (Cockcroft-Gault)

Creatinine clearance (CrCl) estimates the glomerular filtration rate (GFR), the rate at which the kidneys filter blood, using serum creatinine levels, age, weight, and sex. It is not what labs report as kidney function any more (that is eGFR, from the CKD-EPI equation), but it is still what most drug labels and dosing references are written against, which is why pharmacists keep calculating it.

Cockcroft-Gault formula (most widely used clinically):

CrCl (mL/min) = [(140 − Age) × Weight (kg)] / [72 × Serum Creatinine (mg/dL)]
× 0.85 for females (women have lower muscle mass and thus lower creatinine production)

Kidney function stages by GFR/CrCl:

These are the KDIGO stages, written for eGFR per 1.73 m² of body surface. CrCl is plain mL/min for this body, so the stage is a rough guide here. Drug labels set their own CrCl cut-offs, most often at 30, 50 or 60 mL/min.

The eGFR equations, for comparison:

Labs now report eGFR from CKD-EPI 2021, which has no race term and no weight. The older MDRD equation carried a 1.212 multiplier for Black patients; that race coefficient has been dropped in the US since the 2021 NKF-ASN recommendation. The GFR calculator runs both.

Drug dosing implications:

Renal clearance affects: antibiotics (vancomycin, aminoglycosides), anticoagulants (enoxaparin, and the DOACs dabigatran, rivaroxaban, apixaban and edoxaban, whose trials and labels used Cockcroft-Gault), antivirals (acyclovir, tenofovir), and many cardiac drugs. For the drugs that harm the kidneys as well as leaving through them, vancomycin and the aminoglycosides above all, dosing follows measured drug levels, not only the creatinine.

Worked example:

Patient: 68-year-old male, weight 80 kg, serum creatinine 1.4 mg/dL.
CrCl = [(140 − 68) × 80] / [72 × 1.4]
= [72 × 80] / [100.8]
= 5,760 / 100.8
= 57.1 mL/min → Stage G3a (mildly to moderately decreased kidney function)

A vancomycin dose that would be appropriate for normal kidneys would require significant reduction at this CrCl to prevent drug accumulation and nephrotoxicity.

Important: Creatinine-based estimates are less reliable in elderly, malnourished, or obese patients. Cystatin C-based eGFR is preferred in these populations.

Obesity adjustment. Cockcroft-Gault uses weight as a proxy for muscle mass, and overestimates CrCl in obese patients because adipose tissue produces little creatinine. When actual body weight exceeds ideal body weight (IBW) by more than 30%, the convention is to substitute an adjusted body weight in the formula: ABW = IBW + 0.4 × (actual weight − IBW). The IBW itself comes from the Devine formula (men: 50 + 2.3 × inches over 60; women: 45.5 + 2.3 × inches over 60). For underweight patients, use actual body weight rather than IBW, because substituting upward never helps the estimate. The calculator above applies all of this once you give it a height.

A common pitfall: “normal” creatinine is not always normal kidney function. A frail elderly patient or a malnourished one produces less creatinine because they have less muscle, so the serum value reads in the normal range even when CrCl is genuinely poor. A creatinine of 0.8 mg/dL in a 90-year-old can correspond to a CrCl below 30 mL/min. This is the case where Cystatin C is the better marker.