Creatinine Clearance Calculator
Creatinine clearance (CrCl) estimates glomerular filtration rate from age, weight, serum creatinine, and sex. The Cockcroft-Gault equation remains the standard for adjusting renally cleared medication doses in clinical practice.
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Formula
CrCl = (140 − Age) × Weight (kg) ÷ (72 × Creatinine) × [0.85 if female]
The numerator (140 − age) captures the natural decline in kidney filtration with age. Weight reflects the muscle mass that produces creatinine — higher weight generally means more muscle and higher creatinine production. Dividing by 72 × serum creatinine normalizes for the relationship between serum creatinine concentration and filtration. The female correction factor of 0.85 accounts for women's generally lower muscle mass (and thus lower creatinine production) relative to men of the same weight.
How to use the Creatinine Clearance Calculator
- 1
Enter your age
Value should be in years.
- 2
Enter your body weight
Value should be in kg.
- 3
Enter your serum creatinine
Value should be in mg/dL.
- 4
Enter your gender
- 5
Read your results instantly
Results update in real time as you type.
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What creatinine clearance means clinically
CrCl above 90 mL/min is normal kidney function. Values of 60–89 indicate mildly reduced function. 30–59 is moderately reduced, 15–29 severely reduced, and below 15 is kidney failure requiring dialysis consideration. These thresholds trigger dose adjustments for many common medications: vancomycin, digoxin, metformin, direct oral anticoagulants, and many antibiotics all require reduced doses or contraindications below certain CrCl thresholds. This makes accurate CrCl estimation critical for medication safety.
Limitations of the Cockcroft-Gault equation
The equation was developed in 1976 from a relatively small cohort and has known limitations. It overestimates CrCl in obese patients (using adjusted body weight is recommended), underestimates in elderly patients with very low muscle mass, and is less accurate in rapidly changing kidney function (e.g., acute kidney injury). Modern alternatives like MDRD and CKD-EPI are more accurate for staging chronic kidney disease, but Cockcroft-Gault remains the FDA-recommended equation for drug dosing decisions. Actual 24-hour urine creatinine clearance collection remains the clinical gold standard.
Tips & Insights
Use ideal body weight for obese patients
For patients who are significantly obese, using ideal body weight or adjusted body weight (IBW + 0.4 × [actual − IBW]) in the Cockcroft-Gault equation prevents overestimation of kidney function and medication overdose.
Creatinine changes lag behind actual kidney function
In acute kidney injury, serum creatinine rises slowly — kidney function can deteriorate significantly before creatinine reflects it. In this setting, the Cockcroft-Gault equation underestimates the degree of impairment.
Recheck after significant weight change or illness
Major changes in body weight, new medications, or acute illness can alter both kidney function and serum creatinine production. Recheck CrCl whenever clinically relevant medication dosing is being evaluated.
Worked Examples
50-year-old male, 70 kg, creatinine 1.0 mg/dL
CrCl ≈ 87.5 mL/min (normal)
75-year-old female, 55 kg, creatinine 1.2 mg/dL
CrCl ≈ 27.0 mL/min (severely reduced)
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Frequently Asked Questions
What is a normal creatinine clearance?
Normal CrCl for adults is generally above 90 mL/min, though it declines naturally with age. A 70-year-old with CrCl of 65 mL/min may have appropriate kidney function for their age.
How does CrCl differ from GFR?
Glomerular filtration rate (GFR) and creatinine clearance are related but not identical. CrCl slightly overestimates true GFR because creatinine is both filtered and secreted by the kidneys. eGFR formulas (MDRD, CKD-EPI) correct for this.
Why does gender affect creatinine clearance?
Women have less muscle mass than men of the same body weight, producing less creatinine. Lower serum creatinine with the same kidney function leads to overestimation of CrCl without the 0.85 correction.
Should I use this for drug dosing decisions?
This calculator is for educational reference. All medication dosing decisions, particularly for drugs with narrow therapeutic windows, should be made by or in consultation with a licensed pharmacist or physician.
Can dehydration affect my creatinine level?
Yes. Dehydration concentrates serum creatinine, making CrCl appear worse than it is. Rehydrating and rechecking creatinine is important before making permanent dose adjustments based on a single reading.
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