Creatinine Clearance Calculator
Introduction: 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.
How to use this creatinine clearance calculator
- Enter the patient’s age in years, weight in kg (using your institution’s weight convention — see the FAQ), sex, and most recent serum creatinine in mg/dL.
- Read the Cockcroft-Gault CrCl result. For CKD staging you generally want eGFR instead — use a dedicated eGFR calculator with the 2021 race-free CKD-EPI equation.
- Cross-check the CrCl against the specific drug’s renal-dosing table — the number is an input to a decision a clinician makes, not the decision itself.
Why creatinine clearance matters for drug dosing
Many medications are cleared by the kidneys, and giving a standard dose to someone whose kidneys filter slowly lets the drug accumulate to toxic levels. That is why renal-dose tables for antibiotics, anticoagulants, antivirals, and chemotherapy agents are written against creatinine clearance thresholds — commonly breakpoints at 50, 30, and 15 mL/min. A patient at 74 mL/min may need no adjustment for one drug and a halved dose for another, so the clearance number is only useful next to a specific drug’s guidance. Cockcroft-Gault endures for this purpose, decades after simpler eGFR equations appeared, precisely because the original pharmacokinetic dosing studies were validated against it; switching to eGFR for dosing can shift a patient across a breakpoint and change the recommended dose. This is also why the estimate is most fragile exactly when it matters most: in acute illness, serum creatinine lags real kidney function by a day or more, so a falling creatinine in recovering acute kidney injury will overstate current clearance and a rising one will understate it. The safe habit is to trend several creatinine values, use the institution’s specified weight convention, and treat the output as a prompt to check the drug reference rather than a standalone verdict.
Creatinine clearance questions clinicians ask
What weight should I use in Cockcroft-Gault?
Clinical practice varies, but a common convention is to use ideal body weight when a patient is at or above their ideal weight, actual body weight when they are underweight, and an adjusted body weight for obesity, because fat tissue generates little creatinine. Using actual weight in an obese patient can substantially overestimate clearance, so match the weight convention your institution's dosing protocol specifies.
Is creatinine clearance the same as eGFR?
No. Cockcroft-Gault CrCl estimates clearance in mL/min and is still specified in many drug package inserts for renal dosing, while eGFR (from the 2021 race-free CKD-EPI equation) estimates GFR normalized to body surface area in mL/min/1.73m² and is used to stage chronic kidney disease. They can differ by 20 percent or more, so use the measure the task calls for.
Why was race removed from kidney-function equations?
The 2021 CKD-EPI creatinine equation dropped the race coefficient because using race as a biological variable was scientifically unjustified and could delay care for Black patients. Major U.S. laboratories and professional societies adopted the race-free equation for eGFR reporting; this page focuses on Cockcroft-Gault CrCl, which never used race.
How accurate is the Cockcroft-Gault estimate?
It is an estimate, not a measurement. It assumes a stable serum creatinine, so it is unreliable in acute kidney injury where creatinine is still rising or falling, and it is affected by muscle mass, diet, and certain drugs that alter creatinine secretion. For critical decisions, clinicians may order a timed urine collection or a measured GFR.
Arcade Mini-Game: Creatinine Clearance Calculator Calibration Run
Use this quick arcade run to practice separating useful scenario inputs from common planning mistakes before you rely on the calculator output.
Start the game, then use your pointer or arrow keys to catch useful inputs and avoid bad assumptions.