🫘 Creatinine Clearance Calculator – Estimate Kidney Filtration Capacity
The Creatinine Clearance Calculator estimates how well your kidneys filter creatinine from the bloodstream, expressed in mL/min. It supports three clinical methods — Cockcroft-Gault for adults, Measured 24-Hour Urine clearance, and the Pediatric Schwartz equation — making it a practical tool for students, clinicians, pharmacists, and patients who need quick renal function estimates without specialized laboratory software.
What Is Creatinine Clearance?
Creatinine is a metabolic waste product of muscle activity. Healthy kidneys continuously filter creatinine from the blood; the rate at which they do so is called creatinine clearance (CrCl). Unlike eGFR (which is indexed to body surface area), CrCl from Cockcroft-Gault is commonly used directly for medication dosing adjustments — particularly for renally cleared drugs such as aminoglycosides, vancomycin, direct oral anticoagulants, and metformin.
CrCl slightly overestimates true glomerular filtration rate (GFR) because creatinine is also actively secreted by renal tubules. Modern eGFR equations (e.g., CKD-EPI 2021) correct for this and are preferred for CKD staging, while Cockcroft-Gault remains the standard reference in many drug dosing references and pharmacokinetic guidelines.
Supported Calculation Methods
1. Cockcroft-Gault (Adult)
The most widely used formula for estimating adult creatinine clearance. Published in 1976, it requires age, biological sex, body weight, and serum creatinine (SCr):
CrCl (male) = ((140 − age) × weight_kg) / (72 × SCr_mg/dL)
CrCl (female) = CrCl (male) × 0.85Three body weight strategies are supported to handle different patient populations:
- Actual Body Weight (ABW) — Used for most patients at or near their ideal weight.
- Ideal Body Weight (IBW, Devine formula) — Preferred when actual weight is at or below IBW, or for lean body mass–based estimates.
- Adjusted Body Weight (AdjBW) — Recommended for overweight or obese patients:
AdjBW = IBW + 0.4 × (ABW − IBW). Using actual weight in obesity may significantly overestimate CrCl.
2. Measured 24-Hour Urine Clearance
This is the most direct method, requiring a timed urine collection (typically 24 hours), urine creatinine concentration, urine volume, and serum creatinine:
Urine flow (mL/min) = Total urine volume (mL) / Collection time (min)
CrCl = (UCr × urine flow) / SCrAccurate collection is critical — incomplete urine collection leads to underestimation. The calculator will display a notice if the collection duration differs from the standard 24-hour period.
3. Pediatric Schwartz Estimate
Designed for children and adolescents, the bedside Schwartz equation estimates GFR from height and serum creatinine alone — no weight needed:
CrCl ≈ (k × height_cm) / SCr_mg/dLThe constant k = 0.413 is the modern bedside value validated for isotope-dilution mass spectrometry (IDMS)–calibrated creatinine assays used in current laboratory practice. Older values (0.55, 0.70) were specific to non-standardized assays and should not be used with modern labs.
BSA Normalization
When enabled, results are normalized to a reference body surface area of 1.73 m² using the Mosteller formula:
BSA (m²) = √((height_cm × weight_kg) / 3600)
Normalized CrCl = CrCl × (1.73 / BSA)Normalized values allow comparison across patients with different body sizes and are commonly reported alongside eGFR values. Patients with unusually small or large body frames may benefit most from this adjustment.
Unit Conversions Supported
| Measurement | Units Accepted | Conversion Factor |
|---|---|---|
| Serum / Urine Creatinine | mg/dL, µmol/L | 1 mg/dL = 88.4 µmol/L |
| Body Weight | kg, lb | 1 kg = 2.2046 lb |
| Height | cm, in | 1 in = 2.54 cm |
| Urine Volume | mL, L | 1 L = 1000 mL |
| Collection Duration | hours, minutes | 1 h = 60 min |
Interpreting Your Result
The calculator provides a qualitative interpretation alongside the numeric result. These bands are commonly used in clinical practice to guide drug dosing and monitoring:
- ≥ 90 mL/min — Normal or high clearance; standard drug doses generally apply
- 60–89 mL/min — Mildly reduced; some renally cleared drugs may need minor adjustment
- 45–59 mL/min — Mildly to moderately reduced; review drug dosing carefully
- 30–44 mL/min — Moderately reduced; many drugs require significant dose reduction or avoidance
- 15–29 mL/min — Severely reduced; specialist review often required
- < 15 mL/min — Kidney failure range; dialysis may be a consideration
Creatinine Clearance vs. eGFR: Key Differences
Though both estimate kidney function, they are not interchangeable for all purposes:
- CrCl (Cockcroft-Gault) is not normalized to BSA, tends to run slightly higher than eGFR, and is the recommended basis for most drug dosing references in the United States and internationally.
- eGFR (CKD-EPI 2021) is indexed to 1.73 m² BSA, more accurate for detecting and staging chronic kidney disease, and preferred for clinical documentation of kidney function.
Clinical Notes and Limitations
All formulas produce estimates, not measurements. Factors that may affect accuracy include:
- Very low or very high muscle mass (e.g., sarcopenia, bodybuilding, amputees) — creatinine production may not reflect kidney function accurately
- Acute kidney injury — creatinine may not yet reflect the true current function
- High-protein diets or creatine supplementation — can transiently elevate SCr
- Certain medications (e.g., trimethoprim, cimetidine) — block tubular creatinine secretion, raising SCr without affecting GFR
- Pregnancy — lower SCr values are expected; standard formulas may overestimate clearance
Always interpret results alongside clinical history, urine studies, and repeat measurements before making medication dosing or clinical management decisions.