Creatinine Clearance Calculator
Understanding creatinine clearance (CrCl)
Creatinine is a waste product formed from normal muscle metabolism. Healthy kidneys remove creatinine from the blood and excrete it into urine. Creatinine clearance (CrCl) is an estimate of how much blood the kidneys can “clear” of creatinine per minute, and it is commonly used as a practical proxy for kidney filtration when making medication dosing decisions.
This calculator uses the Cockcroft–Gault equation, a widely used method in clinical pharmacology because it combines readily available patient factors (age, weight, sex, serum creatinine) to approximate CrCl without a timed urine collection.
The Cockcroft–Gault formula
For serum creatinine in mg/dL and weight in kg, the Cockcroft–Gault estimate is:
- CrCl is typically expressed in mL/min.
- age is in years.
- weight is in kilograms (see notes on which weight to use below).
- SCr is serum creatinine in mg/dL.
- sexFactor is 1.0 for males and 0.85 for females (a historical adjustment reflecting average differences in creatinine generation).
How to interpret the result
The output is an estimate of kidney filtration used most often for drug dosing. Many drug references group dosing recommendations by CrCl ranges. Commonly used (non-diagnostic) categories you may see in medication labeling include:
- ≥ 90 mL/min: often treated as normal/near normal for dosing in many adults
- 60–89 mL/min: mild reduction (dose changes may or may not be needed depending on the drug)
- 30–59 mL/min: moderate reduction (dose adjustment frequently needed)
- 15–29 mL/min: severe reduction (dose adjustment usually needed; some drugs avoided)
- < 15 mL/min: kidney failure range (specialist guidance; dialysis context may apply)
Important: CrCl from Cockcroft–Gault is not the same as laboratory-reported eGFR (often CKD-EPI). Your clinician may prefer one measure over the other depending on the task (e.g., diagnosing/staging CKD vs dosing a specific medication).
Worked example
Example: 60-year-old male, weight 80 kg, serum creatinine 1.2 mg/dL.
- Compute the age term: 140 − 60 = 80
- Multiply by weight and sex factor: 80 × 80 × 1.0 = 6400
- Compute denominator: 72 × 1.2 = 86.4
- CrCl = 6400 / 86.4 = 74.1 mL/min (approx.)
In many drug-dosing references, a CrCl around ~74 mL/min falls into a range where some medications need no change while others recommend dose reduction—so the next step is to consult the specific drug’s renal dosing guidance.
CrCl vs eGFR (comparison)
| Method | Primary common use | Typical inputs | Output units | Common pitfalls |
|---|---|---|---|---|
| Cockcroft–Gault (CrCl) | Medication dosing (many labels and drug databases) | Age, weight, sex, SCr | mL/min | Sensitive to weight choice and muscle mass; less reliable in acute illness/non–steady state |
| CKD-EPI (eGFR) | CKD evaluation/staging and risk stratification (commonly lab-reported) | Age, sex, SCr (sometimes cystatin C) | mL/min/1.73 m² | Indexed to body surface area; may differ from dosing needs; less accurate in non–steady state |
| MDRD (eGFR) | Older CKD estimation method (still seen in some systems) | Age, sex, SCr | mL/min/1.73 m² | Less accurate at higher kidney function; same non–steady state limitations |
Assumptions and limitations (read before using)
- Steady-state creatinine: The equation assumes serum creatinine is stable. In acute kidney injury (rapidly changing creatinine), CrCl estimates can be misleading.
- Adults: Cockcroft–Gault was derived in adults; it is not a pediatric formula.
- Extremes of muscle mass/body habitus: Very muscular, frail, malnourished, amputees, and some neuromuscular conditions can produce unreliable estimates because creatinine production differs from “average.”
- Weight selection matters: Using actual vs ideal vs adjusted body weight can materially change the result. Many drug references specify which weight to use in obesity; follow clinical guidance for the specific medication.
- Pregnancy: Physiologic changes can alter creatinine generation and filtration; specialized assessment is often preferred.
- Creatinine assay differences: Modern standardized assays and lab methods can shift creatinine values compared with those used when the equation was developed, affecting estimates.
- Not a diagnosis: A single estimated CrCl should not be used alone to diagnose CKD or determine prognosis.
Input tips
- Enter serum creatinine in mg/dL. If your lab reports µmol/L, convert using: mg/dL = (µmol/L) ÷ 88.4.
- Use weight in kg. If you have pounds, convert using: kg = lb ÷ 2.2046.
- If your clinician has instructed you to use ideal or adjusted body weight for dosing, use that value here.
Medical disclaimer
This calculator provides an educational estimate and is not medical advice. Dosing and clinical decisions should be made by qualified clinicians using the full clinical context, current guidelines, and the prescribing information for specific medications.