Creatinine Clearance Calculator

Calculate creatinine clearance using Cockcroft-Gault and adjust drug doses for renal impairment.

Serum creatinine (mg/dL) (mg/dL)

Age (years) (years)

Weight (kg) (kg)

Sex

Drug normal dose (mg) (mg)

GFR threshold for dose reduction (mL/min) (mL/min)

Please check your inputs and try again.

Why Serum Creatinine Alone Misleads

Creatinine comes from muscle, so how much appears in blood depends on muscle mass as well as kidney function. A frail elderly woman with "normal" creatinine can have substantially reduced clearance, because she produces little creatinine to begin with.

CrCl = [(140 − age) × weight] / (72 × S_Cr) × 0.85 if female

Every term in Cockcroft–Gault exists to correct for this. Age reduces the estimate because muscle mass declines; weight raises it; and the 0.85 factor accounts for lower average muscle mass in women.

CrCl (mL/min)	CKD stage	Implication
≥ 90	1	Normal
60–89	2	Mildly reduced
45–59	3a	Moderate — review drug doses
30–44	3b	Moderate to severe
15–29	4	Severe — plan for replacement
< 15	5	Kidney failure

Cockcroft–Gault or CKD-EPI?

	Cockcroft–Gault	CKD-EPI
Estimates	Creatinine clearance	GFR
Units	mL/min	mL/min/1.73m² (normalised)
Uses weight	Yes	No
Best for	Drug dosing	Staging CKD

The distinction matters practically. CKD-EPI normalises to body surface area, which is right for classifying disease but wrong for dosing — a drug dose must match the patient's actual clearance, not a size-adjusted figure. Most drug labelling is still based on Cockcroft–Gault, so dose adjustment should use it.

Both estimates assume steady state. In acute kidney injury creatinine lags behind the true fall in filtration by a day or more, so an early value substantially overestimates remaining function.

Worked Examples

Example 1: 65yo male, Cr=1.2, wt=70

CrCl=(140-65)×70/(72×1.2)

Result: CrCl=60.8mL/min — mild reduction

Metformin: reduce if CrCl<45; hold if CrCl<30

Example 2: 80yo female, Cr=1.0, wt=55

CrCl=(140-80)×55/(72×1.0)×0.85

Result: CrCl=39.0mL/min — Stage 3b

Multiple drugs need dose adjustment

Example 3: Why sex correction matters

Same age, weight and creatinine, male versus female

Result: 15% lower estimate in women

The 0.85 factor reflects lower average muscle mass, so a woman produces less creatinine for the same renal function.

Example 4: Normal creatinine, reduced clearance

82-year-old woman, 48 kg, creatinine 1.0 mg/dL

Result: CrCl about 33 mL/min — stage 3b

Creatinine is within the reference range, yet clearance is well below the threshold for adjusting many drug doses.

Common Mistakes

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Using a normal creatinine to exclude kidney impairment

Creatinine production depends on muscle mass. An elderly or cachectic patient can have marked impairment with creatinine in the reference range.

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Using CKD-EPI for drug dosing

CKD-EPI normalises to body surface area, which suits staging but not dosing. Most drug labelling is based on Cockcroft–Gault in mL/min.

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Trusting estimates during acute kidney injury

Creatinine lags the true fall in filtration by a day or more. Early values overestimate function when it is deteriorating rapidly.

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Using actual body weight in obesity

Cockcroft–Gault overestimates clearance in obese patients. Ideal or adjusted body weight is generally preferred.

Frequently Asked Questions

Cockcroft-Gault vs CKD-EPI?

CKD-EPI for classification/staging. Cockcroft-Gault for drug dosing (FDA). Kidney function labels of most drugs use CrCl cutoffs from Cockcroft-Gault. Use actual body weight (or ideal if obese) for CG formula.

Key drugs requiring dose reduction?

Metformin (hold <30), DOAC anticoagulants, renally-cleared antibiotics (aminoglycosides, vancomycin), digoxin, low-MW heparins, gabapentin, many antivirals. Always check product labeling for specific cutoffs.

Why can creatinine be normal despite kidney impairment?

Because it depends on muscle mass. Elderly, frail or cachectic patients produce little creatinine, so serum levels stay in range even as filtration falls.

Should I use Cockcroft–Gault or CKD-EPI for drug dosing?

Cockcroft–Gault. It gives clearance in mL/min matching the patient's actual size, which is what drug labelling is based on. CKD-EPI is normalised and suits staging.

Why is there a correction factor for women?

Lower average muscle mass means less creatinine production for the same renal function, so the uncorrected formula would overestimate clearance.

Are these estimates valid in acute kidney injury?

No. Both assume steady state, and creatinine lags the actual fall in filtration by a day or more.