Creatinine Clearance Calculator

About the Creatinine Clearance Calculator

The Creatinine Clearance Calculator estimates kidney function with the Cockcroft-Gault equation, a long-standing formula still referenced in many drug-dosing recommendations. Unlike eGFR, creatinine clearance (CrCl) is expressed as an absolute flow rate in mL/min rather than normalized to body surface area, which is why many medication labels still point back to it.

The Cockcroft-Gault equation accounts for age, weight, sex, and serum creatinine. It is useful for understanding the reference number many dosing tables are built around, but it remains an estimate and can be inaccurate in acute kidney injury, unusual body composition, pregnancy, or other settings where serum creatinine is unstable or misleading.

This page helps translate routine demographics and lab values into that estimate so the result can be reviewed in context with eGFR, clinical history, and the specific medication guidance being used.

When This Page Helps

Creatinine clearance is useful because many renally cleared drug labels and pharmacy protocols still reference Cockcroft-Gault cutoffs rather than eGFR. If you want to understand why a dose adjustment threshold is written as 50 or 30 mL/min, CrCl is usually the number behind it.

It should still be interpreted as an estimate rather than a direct measurement. The calculator is best used to understand the dosing reference point, not to replace clinician or pharmacist review of the full medication context.

How to Use the Inputs

1. Enter your serum creatinine from your blood test (mg/dL).
2. Enter your age in years.
3. Enter your actual body weight in kg (or lbs with conversion).
4. Select your sex.
5. View your estimated creatinine clearance.
6. Check common drug dosing thresholds.
7. Discuss results with your pharmacist or physician.

Example Calculation

Tips & Best Practices

• The Cockcroft-Gault equation was developed in 1976 using actual body weight — use it the same way for consistency.
• For obese patients (>130% IBW), some clinicians use adjusted body weight to avoid overestimating CrCl.
• CrCl slightly overestimates true GFR because creatinine is both filtered and secreted by the kidneys.
• Always check your specific drug's prescribing information for its CrCl-based dosing thresholds.
• Muscle mass affects creatinine. Elderly, malnourished, or amputee patients may get falsely reassuring CrCl values.
• A minimum serum creatinine of 0.7–1.0 is sometimes used for elderly patients with very low creatinine to avoid overestimation.

History of the Cockcroft-Gault Equation

Donald Cockcroft and Henry Gault published their landmark equation in 1976 based on data from 249 male patients at Queen Mary Veterans Hospital in Montreal. The formula was remarkably simple yet effective, using readily available clinical data. Despite being nearly 50 years old, it remains the primary method for drug dosing adjustments because virtually all pharmacokinetic studies reference it.

When Cockcroft-Gault Is Less Accurate

The equation is less reliable in: extremes of body weight (very obese or cachectic), acute kidney injury (creatinine not at steady state), pregnancy, patients with limb amputations, and those on creatinine-altering medications (trimethoprim, cimetidine). In these cases, a timed urine collection for measured CrCl or cystatin C-based estimates may be preferable.

CrCl for Drug Dosing in Practice

Pharmacists routinely calculate CrCl for renally-cleared medications. Common CrCl thresholds are <50, <30, and <15 mL/min, with dose reductions or contraindications at each level. Some protocols also specify maximum doses per CrCl range. Always consult current drug monographs for the latest recommendations.

Frequently Asked Questions

• What is creatinine clearance?

  Creatinine clearance (CrCl) is a measure of how quickly creatinine is removed from the blood by the kidneys. It estimates the rate at which the kidneys filter blood, expressed in mL per minute. It closely approximates the glomerular filtration rate and is the standard for drug dosing decisions.

• How is CrCl different from eGFR?

  CrCl is measured in absolute mL/min and depends on patient size. eGFR is normalized to a standard body surface area (1.73 m²). Drug dosing studies overwhelmingly used Cockcroft-Gault CrCl, so most drug labels reference CrCl. For clinical staging of CKD, eGFR (CKD-EPI) is preferred.

• Why does sex affect the calculation?

  The 0.85 factor for females accounts for lower creatinine production due to generally lower muscle mass. Without this correction, CrCl would be overestimated in women because their baseline creatinine production is lower per kilogram of body weight.

• Should I use actual body weight or ideal body weight?

  The original Cockcroft-Gault study used actual body weight. For obese patients, using actual weight may overestimate CrCl. Many pharmacists use adjusted body weight (IBW + 0.4 × [Actual − IBW]) for patients more than 130% of IBW. For underweight patients, actual weight is appropriate.

• What drugs commonly need CrCl-based dose adjustment?

  Common medications with CrCl cutoffs include: metformin (hold if <30), enoxaparin (adjust <30), dabigatran (adjust <50), gabapentin/pregabalin (adjust <60), vancomycin (dose by CrCl), aminoglycosides, and many antibiotics. Always check individual drug labels.

• Is this calculator accurate for children?

  No, the Cockcroft-Gault equation was developed for adults aged 18 and older. For pediatric patients, the Schwartz equation is used to estimate GFR. The original study population was adult males, with the female correction factor added later.