Creatinine Clearance
Estimate creatinine clearance with the Cockcroft-Gault equation, in mL/min.
Cockcroft-Gault is the equation most drug labels use for renal dose adjustment.
Cockcroft-Gault multiplies (140 − age) by weight in kilograms and divides by 72 times the serum creatinine in mg/dL, then multiplies by 0.85 for female patients. For a 60-year-old man of 70 kg with a creatinine of 1.0 mg/dL: (80 × 70) ÷ 72 = 77.8 mL/min.
What creatinine clearance estimates
Creatinine is a waste product of muscle metabolism, produced at a fairly steady rate and cleared almost entirely by the kidneys. If the kidneys slow down, creatinine accumulates in the blood — so a serum creatinine level, read alongside age, sex, and body size, gives an estimate of how much plasma the kidneys are clearing each minute.
The Cockcroft-Gault equation, published in 1976, remains in daily use for one specific reason: most drug labels express their renal dose adjustments in terms of creatinine clearance calculated this way. Even where a laboratory reports an eGFR from a newer equation, the pharmacist adjusting a dose will often want the Cockcroft-Gault figure because that is what the licensing studies used.
Age, weight, and sex in the equation
Clearance falls with age, which the (140 − age) term captures. It rises with body size, because larger people have more muscle and clear more — hence multiplying by weight. And the 0.85 factor for women reflects a lower average muscle mass for the same body weight. These are population averages, which is exactly why the result is an estimate rather than a measurement.
Creatinine in µmol/L is divided by 88.4 to convert to mg/dL. The equation was derived using actual body weight.
Worked example: 60-year-old man, 70 kg, creatinine 1.0 mg/dL
Work the numerator, then the denominator, then divide:
- 1 Convert the creatinine to mg/dL if needed. A result in µmol/L is divided by 88.4 — 88 µmol/L is 1.0 mg/dL.
- 2 Subtract the age from 140. 140 − 60 = 80.
- 3 Multiply by the weight in kilograms. 80 × 70 kg = 5600.
- 4 Multiply the creatinine by 72. 72 × 1.0 mg/dL = 72.
- 5 Divide. 5600 ÷ 72 = 77.8 mL/min.
- 6 Apply the sex factor. For a female patient multiply by 0.85. This patient is male, so 77.8 mL/min stands.
Cockcroft-Gault estimates at 70 kg
Calculated with the formula above for a 70 kg patient, rounded to one decimal place. Female values include the 0.85 factor.
| Age | Creatinine 0.8 mg/dL | Creatinine 1.0 mg/dL | Creatinine 1.5 mg/dL | Creatinine 2.0 mg/dL |
|---|---|---|---|---|
| 30, male | 133.7 | 106.9 | 71.3 | 53.5 |
| 30, female | 113.6 | 90.9 | 60.6 | 45.5 |
| 50, male | 109.4 | 87.5 | 58.3 | 43.8 |
| 50, female | 93.0 | 74.4 | 49.6 | 37.2 |
| 70, male | 85.1 | 68.1 | 45.4 | 34.0 |
| 70, female | 72.3 | 57.8 | 38.6 | 28.9 |
Where the estimate breaks down
Cockcroft-Gault assumes a steady state. In acute kidney injury the serum creatinine lags behind what the kidneys are actually doing, so a normal-looking result can accompany a sharply falling clearance. The equation also inherits the assumption that muscle mass tracks body weight, which fails at the extremes: it tends to overestimate clearance in obesity and in oedema, and to overestimate it in people with very low muscle mass, including many elderly and immobile patients.
Because the estimate is used to reduce drug doses, an overestimate is the dangerous direction — it leaves a patient on a full dose their kidneys cannot clear. Where the picture is unclear, protocols often specify which body weight to use, or call for a different equation entirely.
This tool is an informational estimate for study and practice, not medical advice. Renal dose adjustment must be made by a qualified professional using current laboratory values.