Estimate kidney function using the Cockcroft–Gault equation. Includes CKD staging, unit toggles, and clinical interpretation. Not a substitute for medical advice.
Female results multiplied by 0.85
Valid range: 1–120 years
Actual body weight (not ideal)
Normal: 0.7–1.3 mg/dL (61.9–114.9 μmol/L)
Male, 50yr, 70kg, SCr 1.0 → ≈87.5 mL/min
Female, 60yr, 60kg, SCr 1.1 → ≈53.4 mL/min
Male, 72yr, 80kg, SCr 2.5 → ≈26.1 mL/min (G4)
Female, 45yr, 55kg, SCr 0.8 → ≈85.5 mL/min
CrCl / eGFR (mL/min/1.73m²) direction: left to right
| Stage | CrCl / GFR Range | Description | Action |
|---|---|---|---|
| G1 | ≥ 90 mL/min | Normal or high | Annual monitoring if risk factors present |
| G2 | 60–89 mL/min | Mildly decreased | Monitor every 6–12 months |
| G3a | 45–59 mL/min | Mild–moderate decrease | Nephrology referral, review medications |
| G3b | 30–44 mL/min | Moderate–severe decrease | Active nephrology management |
| G4 | 15–29 mL/min | Severely decreased | Prepare for renal replacement therapy |
| G5 | < 15 mL/min | Kidney failure | Dialysis or transplant evaluation |
Creatinine clearance (CrCl) tells you how efficiently your kidneys are filtering creatinine — a waste product your muscles naturally produce — from your blood every minute. Think of it as a speedometer for kidney filtration: the higher the number, the better your kidneys are working. A healthy adult produces creatinine at a steady rate, so measuring how fast the kidneys remove it gives a reliable window into overall kidney performance.
The most widely used estimation method is the Cockcroft–Gault equation, developed in 1976 and still the gold standard for drug dosing calculations worldwide. Unlike eGFR (which is body-surface-area adjusted), Cockcroft–Gault gives a raw mL/min figure that pharmacists and physicians plug directly into dosing tables for antibiotics, anticoagulants, and chemotherapy agents.
The equation accounts for four variables that predict creatinine production and excretion:
The term captures the fact that muscle mass — and therefore creatinine production — naturally declines with age. Weight accounts for body mass (though ideal body weight is sometimes substituted in obese patients). The 0.85 female correction reflects that women typically have less muscle mass than men of the same weight, so they produce less creatinine at baseline.
Worked example: A 55-year-old male, 80 kg, SCr 1.2 mg/dL: — consistent with mild CKD G2.
Medical Disclaimer
This tool is for educational purposes only. It does not constitute medical advice. Creatinine clearance estimates have inherent limitations and should always be interpreted by a qualified healthcare professional in the context of the full clinical picture.
CrCl = [(140 − age) × weight (kg)] ÷ [72 × SCr (mg/dL)], multiplied by 0.85 for women. Worked example — a 67-year-old woman, 70 kg, serum creatinine 1.2 mg/dL: (140 − 67) × 70 = 5,110; divide by 72 × 1.2 = 86.4 → 59.1; × 0.85 = 50 mL/min. That single number sits below several drug-label cutoffs (see the table below), which is exactly why pharmacies still compute Cockcroft–Gault rather than reading the lab’s eGFR — the 1976 equation is what the FDA dosing studies used.
| CrCl (mL/min) | Interpretation | Typical dosing implications |
|---|---|---|
| ≥ 90 | Normal renal function | Standard dosing for most drugs |
| 60–89 | Mildly reduced | Usually standard dosing; monitor nephrotoxic drugs |
| 30–59 | Moderately reduced | Reduce/space many antibiotics; DOAC dose checks (e.g. rivaroxaban 15 mg for AF at 15–50) |
| 15–29 | Severely reduced | Metformin contraindicated below 30; avoid dabigatran; renal-dose most antimicrobials |
| < 15 | Kidney failure range | Specialist/pharmacist-guided dosing; many agents avoided |
Illustrative label thresholds — always confirm against the current prescribing information for the specific drug.
Lab reports print eGFR (CKD-EPI), normalized to 1.73 m² of body surface area and intended for CKD staging. CrCl (Cockcroft–Gault) uses your actual weight and returns absolute mL/min — the unit drug labels are written in. The two can disagree by 10–20%, and more at weight extremes: in a 120 kg patient, Cockcroft–Gault with total body weight can overestimate clearance substantially (pharmacists often substitute adjusted body weight), while in an 80-year-old with low muscle mass both equations overestimate true function because creatinine production is low. Use our eGFR calculator for staging questions and this page for dosing-style estimates.
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