Creatinine Clearance Calculator

Evaluate kidney function using Cockcroft-Gault formula for drug dosage adjustments

Age (years)

Weight (kg)

Serum Creatinine (mg/dL)

Gender

Frequently Asked Questions

1. What is the difference between creatinine clearance and GFR?

Creatinine Clearance (CrCl) and Glomerular Filtration Rate (GFR) both assess kidney function but are calculated differently. CrCl uses the Cockcroft-Gault formula based on serum creatinine, age, weight, and gender. GFR commonly uses MDRD or CKD-EPI formulas and considers additional factors like race. In clinical practice, values are similar, but CrCl is more often used for drug dosage adjustments, while GFR is preferred for CKD staging and diagnosis.

2. Who is the Cockcroft-Gault formula suitable for?

Suitable for adults aged 18-110, stable weight patients, and those with relatively stable kidney function. NOT suitable for pregnant women (significant muscle mass changes), severely malnourished or obese patients, amputees (reduced muscle mass), patients with acute kidney function changes, or children (use pediatric formulas). The formula requires clinical judgment for special populations.

3. How should CrCl be calculated for obese patients?

For obese patients (BMI > 30), using actual body weight may overestimate CrCl. Clinicians commonly use adjusted methods: (1) Ideal Body Weight (IBW) based on height, (2) Adjusted body weight: IBW + 0.4 × (actual weight - IBW), (3) Lean body weight for more precise estimation. Obese patient CrCl calculation should be determined by doctors or pharmacists based on individual circumstances.

4. Does normal serum creatinine mean normal kidney function?

Not necessarily. Serum creatinine levels are influenced by multiple factors: muscle mass (elderly, women, muscle atrophy patients may have lower creatinine), diet (vegetarians may have lower creatinine, high meat intake may increase it), and renal compensation (in early kidney disease, remaining nephrons can compensate by increasing filtration). Therefore, even with "normal" serum creatinine, elderly, low muscle mass, or high-risk populations should calculate CrCl or eGFR for accurate kidney function assessment.

5. Which common medications require dosage adjustment based on CrCl?

Many medications require renal dose adjustment: Antibiotics (vancomycin, aminoglycosides, some cephalosporins), Anticoagulants (dabigatran, rivaroxaban, apixaban), Diabetes medications (metformin - contraindicated if eGFR < 30), Chemotherapy drugs (carboplatin, methotrexate), Antivirals (acyclovir, ganciclovir), Analgesics (certain opioids). Specific dose adjustments should be consulted with doctors or pharmacists.

6. What are the clinical applications of creatinine clearance?

CrCl has multiple clinical applications: (1) Drug dosage adjustment - many drugs require dose adjustment based on renal function, CrCl < 30 mL/min usually needs significant adjustment. (2) Kidney function assessment - diagnosing and monitoring acute and chronic kidney disease, evaluating disease progression. (3) Contrast agent use - patients with CrCl < 60 mL/min need risk assessment and hydration to prevent contrast nephropathy. (4) Surgical risk assessment - preoperative kidney function evaluation to predict postoperative complications. (5) Dialysis indication - CrCl < 15 mL/min may require dialysis preparation. (6) Drug toxicity monitoring - certain drugs accumulate in renal insufficiency.

The Cockcroft-Gault equation estimates creatinine clearance, a measure of how quickly the kidneys clear a waste product called creatinine from the blood, using age, weight, sex, and a serum creatinine result. It has been used for decades, particularly to guide drug dosing, though most clinical laboratories now prioritize a related but different measure called estimated glomerular filtration rate (eGFR) for diagnosing and staging kidney disease.

The formula

CrCl (mL/min) = [(140 - age) x weight (kg)] / [72 x serum creatinine (mg/dL)], multiplied by 0.85 for women

age in years
weight in kilograms, typically actual body weight
serum creatinine in mg/dL from a recent blood test
the 0.85 factor adjusts for the generally lower average muscle mass, and therefore lower creatinine production, in women

Cockcroft DW, Gault MH. Nephron, 1976

How the calculation works

Creatinine is a breakdown product of muscle metabolism that the kidneys filter out of the blood at a fairly constant rate. Because creatinine production depends on muscle mass, a given serum creatinine level means something different in a large, muscular young man than in a small, older woman; the Cockcroft-Gault equation adjusts for this using age, weight, and sex alongside the measured creatinine.

The equation multiplies a term based on age and weight by a constant, then divides by 72 times the serum creatinine. Older age lowers the estimate, since the term (140 minus age) shrinks, reflecting the average decline in kidney function with age; higher weight raises the estimate, reflecting greater assumed muscle mass and creatinine production; and a higher measured creatinine lowers the estimate, since creatinine builds up in the blood when the kidneys clear it more slowly.

How to read your result

Creatinine clearance from this equation is often interpreted using the same stage boundaries laboratories use for eGFR, expressed in mL/min, although the two measurements are not identical and can diverge, particularly at the extremes of body size.

Result (mL/min)	Stage	General interpretation
90 and above	Normal or high	Normal kidney function if no other markers of kidney damage
60-89	Mildly reduced	May be normal for age, or early kidney disease if other damage markers are present
30-59	Moderately reduced	Consistent with moderate chronic kidney disease
15-29	Severely reduced	Consistent with severe chronic kidney disease
Below 15	Kidney failure	Consistent with kidney failure; specialist care usually indicated

Cockcroft-Gault versus CKD-EPI

Cockcroft-Gault estimates creatinine clearance, which runs somewhat higher than true glomerular filtration rate because creatinine is not only filtered by the kidneys but also actively secreted by the renal tubules. For diagnosing and staging chronic kidney disease, most laboratories and guideline bodies now report eGFR using the CKD-EPI creatinine equation instead, which was developed and validated on larger, more contemporary populations and correlates better with directly measured GFR.

In 2021, the CKD-EPI creatinine equation was revised to remove the race coefficient that earlier versions included, following a recommendation from a joint National Kidney Foundation and American Society of Nephrology task force that concluded race should not be used as a proxy for biological differences in kidney function. Cockcroft-Gault remains in use mainly because many drug labels and dosing references were built around it decades ago, so it still appears in prescribing guidance even though CKD-EPI is preferred for diagnosis and monitoring. CKD-EPI also reports eGFR normalized to a standard body surface area of 1.73 m2, which makes it comparable across people of different sizes, while Cockcroft-Gault's output is a raw, unnormalized clearance for that specific person's body weight; the two are answering related but distinct questions, which is part of why a drug-dosing calculation and a CKD stage can disagree for the same patient on the same day.

Converting units and adjusting for body weight

Many countries outside the United States report serum creatinine in micromoles per liter (umol/L) rather than mg/dL. To convert before using this formula, divide a umol/L value by 88.4 to get mg/dL, or multiply a mg/dL value by 88.4 to get umol/L. Worked example: a 72-year-old woman weighing 60 kg with a serum creatinine of 1.1 mg/dL gives CrCl = [(140-72) x 60] / (72 x 1.1) x 0.85, or about 43.8 mL/min, placing her in the moderately reduced range.

The equation was derived using actual body weight, which becomes a problem in obesity because fat contributes little creatinine and using actual weight can substantially overstate clearance. When actual body weight exceeds roughly 30 percent above ideal body weight, many clinicians substitute an adjusted body weight instead, particularly for narrow therapeutic index drugs where overestimating clearance risks overdosing.

Ideal body weight (Devine formula), men: 50 kg + 2.3 kg for each inch of height over 5 feet
Ideal body weight (Devine formula), women: 45.5 kg + 2.3 kg for each inch of height over 5 feet
Adjusted body weight, used when actual weight exceeds about 30 percent above ideal: ideal body weight + 0.4 x (actual weight - ideal body weight)
For underweight patients, actual body weight is generally used rather than an adjusted or ideal figure

Serum creatinine (mg/dL)	Serum creatinine (umol/L)
0.6	53
0.8	71
1.0	88
1.2	106
1.5	133
2.0	177
3.0	265

Limitations

Cockcroft-Gault systematically overestimates true glomerular filtration rate, often by roughly 10 to 20 percent, because creatinine clearance includes both filtration and tubular secretion of creatinine; the gap grows as kidney function declines.
The equation was derived using actual body weight in a population without significant obesity; in people who are obese, using actual weight can substantially overestimate clearance, while some clinicians substitute an adjusted or ideal body weight without a single agreed-upon method.
It is unreliable in people with very low muscle mass, including amputees, people with muscle-wasting illness, and frail older adults, because low creatinine production from low muscle mass can make kidney function look better than it is.
The equation assumes stable, steady-state kidney function; it should not be used during acute kidney injury or any period when serum creatinine is rising or falling rapidly, since the result will not reflect current clearance.
It has not been validated for children, and pregnancy changes both blood volume and kidney filtration substantially, so this formula is not appropriate during pregnancy.
This is an estimate, not a directly measured clearance; when precise dosing decisions matter, such as for narrow therapeutic index drugs in people with unusual body composition, a directly measured creatinine clearance from a timed urine collection may be used instead.

Frequently asked questions

Is Cockcroft-Gault the same as eGFR?

No. Cockcroft-Gault estimates creatinine clearance in mL/min using weight, while most eGFR equations, including CKD-EPI, use body surface area instead of weight and do not require a weight input. The two numbers are related but usually not identical.

Why do drug dosing charts still use this old formula?

Many drugs were studied and dosed using Cockcroft-Gault decades before CKD-EPI existed, so their prescribing information was written around it. Updating every drug label to a newer equation is a slow process, so both equations remain in clinical use.

What changed with the 2021 update to CKD-EPI?

The 2021 CKD-EPI creatinine equation removed a coefficient that had adjusted results based on reported race. The change followed a national task force review concluding that race is not a reliable biological proxy for muscle mass or creatinine generation.

Why does my weight matter so much in this calculation?

Creatinine is produced by muscle, and weight is used here as a rough proxy for muscle mass. This is also why the formula is less reliable in people whose weight does not reflect their muscle mass, such as people who are obese or who have significant muscle loss.

How do I convert my creatinine result if it's reported in umol/L?

Divide the umol/L value by 88.4 to get mg/dL before using this calculator. For example, a result of 88 umol/L converts to 1.0 mg/dL, and 133 umol/L converts to 1.5 mg/dL.

Should I use actual weight or an adjusted weight if I'm overweight?

Using actual body weight in someone significantly overweight tends to overstate clearance, since fat contributes little creatinine. Many clinicians use an adjusted body weight, calculated as ideal body weight plus 0.4 times the difference between actual and ideal body weight, once actual weight exceeds roughly 30 percent above ideal, though practice varies and this decision is best made with a clinician for dosing purposes.