Creatinine clearance
Example88.8mL/min· 5329 mL/h
Actual body weight
118.1 mL/min
Overestimates clearance in obesity — adipose tissue produces little creatinine.
Ideal body weight
69.3 mL/min
Adjusted body weightConventional
88.8 mL/min
Conventional at BMI ≥ 30 or above 120% of ideal weight.
Normal
Scale: 0–120 mL/min
Salazar-Corcoran (obesity-specific)
95.5 mL/min
A separate equation validated in obese subjects. Do not use at normal weight.
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Use adjusted body weight in the Cockcroft-Gault equation: AdjBW = IBW + 0.4 × (actual weight − IBW), where ideal body weight comes from the Devine formula. Using actual weight in an obese patient substantially overestimates clearance, because adipose tissue produces very little creatinine. Salazar-Corcoran is a validated obesity-specific alternative.
Overview
Cockcroft-Gault makes one large assumption: that creatinine production — and therefore the clearance the kidneys have to perform — scales with body weight. That assumption holds reasonably well in a normal-weight adult. It fails in four predictable ways.
In obesity the extra weight is largely adipose tissue, which produces very little creatinine, so actual weight overestimates clearance. In the elderly muscle mass falls, so a normal serum creatinine can coexist with genuinely reduced clearance. In amputees measured weight understates the muscle mass the equation assumes, so clearance is underestimated. And in children the equation was simply never validated at all.
Obesity
Male: IBW (kg) = 50.0 + 2.3 × (height in inches − 60) Female: IBW (kg) = 45.5 + 2.3 × (height in inches − 60)
Source: Devine BJ. Drug Intell Clin Pharm. 1974;8:650–5.
AdjBW (kg) = IBW + 0.4 × (actual weight − IBW)
Use AdjBW in place of weight in the Cockcroft-Gault equation. The 0.4 factor is the convention for renal dosing.
Source: Bauer LA et al. Clin Pharmacol Ther. 1983;33(4):519–25.
Male: CrCl = [(137 − age) × ((0.285 × wt) + (12.1 × ht m²))] / (51 × Scr) Female: CrCl = [(146 − age) × ((0.287 × wt) + (9.74 × ht m²))] / (60 × Scr)
Developed in obese subjects. Do not apply it to normal-weight patients.
Source: Salazar DE, Corcoran GB. Am J Med. 1988;84(6):1053–60.
| BMI (kg/m²) | Weight basis | Note |
|---|---|---|
| Actual < IBW | Actual | IBW would credit clearance the patient lacks. |
| < 25 | Ideal | The derivation cohort was broadly normal weight. |
| 25–29.9 | Ideal, or adjusted above 120% of IBW | Judgement zone. |
| 30–39.9 | Adjusted | Standard practice for renal dosing. |
| ≥ 40 | Adjusted, consider Salazar-Corcoran | Both estimates carry more uncertainty here. |
55-year-old man, 120 kg, 175 cm, serum creatinine 1.2 mg/dL.
Actual weight → 118.1 mL/min Ideal weight → 69.3 mL/min Adjusted weight → 88.8 mL/min ← conventional
88.8mL/min
Actual weight overestimates by 33%. Across a 50 mL/min spread, that is the difference between three different dosing bands for the same patient.
Age
Apply Cockcroft-Gault as normal in older patients — the (140 − age) term already encodes the expected age-related decline. The difficulty is not the arithmetic, it is the interpretation.
Muscle mass falls with age, so creatinine production falls too. An 84-year-old with a serum creatinine of 0.9 mg/dL — squarely inside the laboratory reference range — can have a clearance in the 30s. Reading the creatinine alone, without calculating, is the classic error.
A widespread convention is to round low serum creatinine values up to 1.0 mg/dL in elderly patients, on the reasoning that a genuinely low creatinine reflects low muscle mass rather than excellent kidney function. It is not a validated adjustment. It can prevent overestimation, but it can equally cause underdosing — of an antibiotic, or of an anticoagulant. The calculator above shows you both figures so the decision is explicit rather than hidden.
Amputation
Estimated pre-amputation weight = measured weight / (1 − missing fraction) Then apply Cockcroft-Gault to that weight.
Divide rather than add a percentage back: the measured weight already represents the remaining fraction of the original body.
Any correction of this kind is an estimate against population averages, and carries real uncertainty. Where the dosing decision is consequential — an aminoglycoside, a chemotherapy agent — a timed urine collection is materially more reliable than any corrected estimate.
| Segment | % of body weight |
|---|---|
| Hand | 0.7% |
| Forearm with hand | 2.3% |
| Entire arm | 5.0% |
| Foot | 1.5% |
| Lower leg with foot (below knee) | 5.9% |
| Entire leg | 16.0% |
Children
Do not use Cockcroft-Gault in children. It was derived in adults, was never validated in a paediatric population, and applying it is a recognised dosing error. The calculator above suppresses the adult equations entirely when age is under 18 — this is deliberate.
eGFR (mL/min/1.73 m²) = 0.413 × height(cm) / Scr(mg/dL)
Validated in children with CKD, roughly ages 1–16, using enzymatic IDMS-traceable creatinine. Neonates require different equations again.
Source: Schwartz GJ, et al. J Am Soc Nephrol. 2009;20(3):629–37.
8-year-old, 128 cm tall, serum creatinine 0.5 mg/dL.
eGFR = 0.413 × height / Scr
= 0.413 × 128 / 0.5
= 52.86 / 0.5105.7mL/min/1.73m²
Normal for age. Note that the result is BSA-indexed — paediatric dosing is usually per kg or per m², not against an absolute clearance.
Two common questions
No. Cockcroft-Gault has never contained a race coefficient. Some older eGFR equations did — MDRD applies a 1.212 multiplier, and the 2009 CKD-EPI equation had a similar term.
The 2021 CKD-EPI equations deliberately removed that coefficient, following the NKF-ASN Task Force recommendation that race, a social rather than biological category, should not be a variable in kidney function estimation. Current guidance is to use the race-free 2021 equations.
Multiply the mL/min result by 60. A clearance of 68 mL/min is 4,080 mL/hour.
Clearance is conventionally reported per minute, and virtually every drug label uses mL/min. Per-hour figures come up in continuous infusion calculations and in some renal replacement therapy contexts, where flow rates are expressed hourly.
The calculator above shows both figures at once, so there is no manual conversion step to get wrong.
Accuracy
More calculators
For the standard adult case use the Cockcroft-Gault calculator. Where creatinine itself is unreliable, the cystatin C equations sidestep muscle mass entirely.
Standard adult creatinine clearance with actual, ideal and adjusted body weight side by side.
Open calculatorCKD-EPI 2021 creatinine, cystatin C and combined equations, plus Schwartz for children and a CrCl comparison.
Open calculatorMeasured clearance from a timed collection, with a collection-adequacy check and BSA normalisation.
Open calculatorUse adjusted body weight: AdjBW = IBW + 0.4 × (actual weight − IBW), then apply Cockcroft-Gault as normal. Using actual weight in an obese patient substantially overestimates clearance, because adipose tissue contributes little to creatinine production. Salazar-Corcoran is a validated obesity-specific alternative.
You will overestimate creatinine clearance, potentially by a wide margin, and may overdose a renally cleared drug. Cockcroft-Gault assumes creatinine production scales with body weight, which fails in obesity. Compare all three weight bases in the calculator above to see the size of the difference.
Conventionally at a BMI of 30 kg/m², or when actual weight exceeds roughly 120–130% of ideal body weight, whichever is reached first. Below that threshold ideal body weight is generally used. These cut-offs are practice convention rather than a validated rule, and vary between institutions.
You do not apply a race adjustment. Cockcroft-Gault never contained one, and the 2021 CKD-EPI equations deliberately removed the race coefficient that earlier MDRD and CKD-EPI versions used. Current NKF/ASN guidance is that race should not be a variable in kidney function estimation.
Estimate the patient’s pre-amputation weight by correcting for the missing limb mass, then apply Cockcroft-Gault to that figure. Standard limb contributions are roughly 16% for a whole leg, 5% for a whole arm and 1.5% for a foot. Any estimate carries real uncertainty — a timed urine collection is more reliable.
Do not use Cockcroft-Gault — it was never validated in children. Use the bedside Schwartz equation instead: eGFR (mL/min/1.73 m²) = 0.413 × height in cm / serum creatinine in mg/dL (Schwartz et al., JASN 2009). Neonates require different equations again.
Apply Cockcroft-Gault as normal, but interpret it carefully. Reduced muscle mass means an older patient can have a normal serum creatinine alongside genuinely reduced clearance. Rounding a low serum creatinine up to 1.0 mg/dL is a common practice but is not validated and can underestimate clearance.
Multiply the result in mL/min by 60. A CrCl of 68 mL/min is 4,080 mL/hour. Clearance is conventionally reported per minute, but per-hour figures are sometimes needed for continuous infusion and renal replacement calculations. The calculator on this page shows both.
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