Creatinine Clearance Calculator

Introduction: Estimating Creatinine Clearance for Drug Dosing

This calculator estimates creatinine clearance (CrCl) using the Cockcroft-Gault formula, from age, body weight, sex, and serum creatinine. It is the calculation most commonly embedded in drug-dosing tables — the estimate clinicians use to adjust doses of many medications that are cleared by the kidneys.

Creatinine clearance estimates how well the kidneys filter creatinine, a waste product of muscle metabolism. The Cockcroft-Gault equation, published in 1976 by Donald Cockcroft and Henry Gault, was derived from a study of 249 patients aged 18 to 92 and predicts creatinine clearance from age, weight, sex, and serum creatinine. It includes a 15% reduction for females, reflecting their typically lower muscle mass relative to body weight[cockcroft-gault-1976].

The distinction from estimated GFR (eGFR) matters. eGFR (typically the CKD-EPI equation) is normalized to a standard body surface area of 1.73 m² and is the recommended measure for staging chronic kidney disease. Cockcroft-Gault, by contrast, is not normalized — it uses actual body weight and returns a value in mL/min that reflects the individual's size. This makes it the formula historically used for dosing renally-cleared drugs, because a drug dose depends on the actual clearance capacity, not a size-normalized value[cockcroft-gault-1976][niddk-ckd].

This is an educational tool, not a diagnosis. Drug dosing decisions must be made by a qualified healthcare professional using the complete clinical picture.

Creatinine clearance is one piece of the renal and metabolic picture this site covers. The GFR Calculator estimates glomerular filtration rate with the more modern CKD-EPI equation, the Corrected Calcium Calculator addresses the electrolyte disturbances that can accompany renal impairment, and the QTc Calculator monitors the heart-rhythm risk of drugs that accumulate when clearance is reduced. The BMI Calculator provides the body-composition baseline used in interpreting dose adjustments.

How to Use: Finding Creatinine Clearance

Enter age, weight, sex, and serum creatinine, and the result updates instantly.

1. Age (years) — Cockcroft-Gault is validated in adults.
2. Weight (kg) — uses actual body weight (not ideal/adjusted, not normalized).
3. Serum creatinine (mg/dL) — from a recent blood test. If your lab reports in μmol/L, divide by 88.4 to get mg/dL.
4. Sex — applies the 0.85 female factor.

Example 1 — the standard case. Male, 70 years, 80 kg, serum creatinine 1.5 mg/dL. CrCl = ((140 − 70) × 80) / (72 × 1.5) = 5600 / 108 = 51.9 mL/min (no female factor).

Example 2 — female. Female, 70 years, 80 kg, serum creatinine 1.5 mg/dL. CrCl = 51.9 × 0.85 = 44.1 mL/min. The female factor reduces the estimate because of lower average muscle mass relative to weight[cockcroft-gault-1976].

Example 3 — younger adult. Male, 40 years, 75 kg, serum creatinine 1.0 mg/dL. CrCl = ((140 − 40) × 75) / (72 × 1.0) = 7500 / 72 = 104.2 mL/min — a normal clearance for a younger adult.

The Formula: Cockcroft-Gault

The Cockcroft-Gault equation estimates creatinine clearance in mL/min:

where the sex factor is 0.85 for females and 1.0 for males[cockcroft-gault-1976].

Important: this formula requires serum creatinine in mg/dL. If your lab reports creatinine in μmol/L, convert by dividing by 88.4 before entering it.

A Worked Example: 70-Year-Old Male, 80 kg, Creatinine 1.5

Step 1 — gather inputs. Age 70, weight 80 kg, serum creatinine 1.5 mg/dL, male.

Step 2 — compute the numerator. (140 − 70) × 80 = 70 × 80 = 5600.

Step 3 — compute the denominator. 72 × 1.5 = 108.

Step 4 — divide. 5600 / 108 = 51.9 mL/min.

Step 5 — apply the sex factor. Male → × 1.0 → 51.9 mL/min.

Step 6 — interpret. A CrCl of ~52 mL/min suggests moderately reduced renal clearance. For drug dosing, many references use ranges (e.g., >50, 30–50, <30 mL/min) to guide dose adjustment — a clinician applies the relevant drug's specific criteria[fda-renal].

Reference Table: How CrCl Varies with Inputs

The table shows how creatinine clearance changes with age, weight, sex, and creatinine (serum creatinine 1.0 mg/dL unless noted):

Two patterns stand out. First, clearance declines with age — the (140 − age) term means each year of age lowers the estimate. Second, the female factor (0.85) and a higher serum creatinine both reduce the estimate substantially, which is why weight and accurate creatinine matter so much for drug dosing[cockcroft-gault-1976].

Practical Tips: Using Cockcroft-Gault Correctly

• Use real body weight — usually. Cockcroft-Gault was derived with actual body weight. At extremes of obesity or cachexia, ideal or adjusted body weight may be more appropriate; many references advise adjusted weight for BMI >30[fda-renal].
• Convert units first. The formula requires creatinine in mg/dL. If your lab uses μmol/L, divide by 88.4. A unit error changes the result by ~88×.
• Know which formula is being used. CrCl (Cockcroft-Gault) and eGFR (CKD-EPI) are different numbers answering different questions. Dosing tables usually specify which one they assume — match them[awdishu-2025].
• Requires steady-state creatinine. The formula is invalid in acute kidney injury or rapidly changing kidney function, where creatinine has not reached equilibrium[niddk-ckd].
• Not validated under 18. Cockcroft-Gault was derived in adults; pediatric kidney function is estimated differently.
• KDIGO 2024 prefers CKD-EPI for staging and increasingly for dosing. Use this calculator for context, but follow current institutional guidance on which formula to apply for a specific drug[kdigo-2024].
• Match the dosing-table units. A dosing table that says "reduce dose if CrCl < 30" is almost always referring to Cockcroft-Gault in mL/min; one that says "eGFR < 30" refers to CKD-EPI in mL/min/1.73 m². Read the drug's label to see which measure it uses, and enter the matching inputs[fda-renal].
• Re-check creatinine on changes in status. Because the formula requires a steady state, a creatinine drawn during an acute illness or after starting or stopping a medication that affects it may not reflect the patient's baseline. A clinician should re-evaluate with a fresh creatinine when kidney function may have changed[niddk-ckd].

Limitations: What This Calculator Does Not Do

• It is not a diagnosis and not a dosing order. It estimates creatinine clearance; it does not recommend a specific drug dose. Dose adjustment requires a clinician applying the drug's approved criteria[fda-renal].
• Cockcroft-Gault is not normalized to body surface area. It overestimates clearance in obesity and underestimates it in low muscle mass, because it depends on total body weight.
• It assumes a steady state. In acute kidney injury, rapidly changing creatinine, or unstable patients, the estimate is unreliable[niddk-ckd].
• It predates modern creatinine standardization. Cockcroft-Gault was developed before IDMS-calibrated creatinine assays; modern CKD-EPI is calibrated to IDMS standards, so results may differ between the two formulas for the same patient[inker-2021].
• KDIGO 2024 recommends CKD-EPI over Cockcroft-Gault in many settings. This calculator is provided for the many drug tables that still reference Cockcroft-Gault, but it is not the preferred general measure of kidney function[kdigo-2024].
• Not for children, pregnancy, or extremes of body habitus without clinician guidance. Pediatric renal function is estimated with age-adjusted equations, and pregnancy changes kidney function substantially.

Frequently Asked Questions

❓ What is creatinine clearance?

✅ Creatinine clearance estimates how well the kidneys filter creatinine, a waste product of muscle metabolism. It is expressed in mL/min and is used primarily for dosing drugs that are cleared by the kidneys. The Cockcroft-Gault formula estimates it from age, weight, sex, and serum creatinine.

❓ What is the Cockcroft-Gault formula?

✅ CrCl = ((140 − age) × weight in kg) / (72 × serum creatinine in mg/dL), multiplied by 0.85 for females and 1.0 for males. It was published in 1976 and is widely used in drug-dosing tables.

❓ What is the difference between creatinine clearance and eGFR?

✅ Creatinine clearance (Cockcroft-Gault) is not normalized to body surface area and reflects actual clearance for drug dosing. eGFR (CKD-EPI) is normalized to 1.73 m² and is used for staging chronic kidney disease. They answer different clinical questions and can give different numbers.

❓ Why is there a female factor in Cockcroft-Gault?

✅ Because, on average, females have lower muscle mass relative to body weight, and creatinine comes from muscle. The original study found creatinine clearance about 15% lower in females, so the formula applies a 0.85 factor.

❓ What is a normal creatinine clearance?

✅ There is no single 'normal' value; clearance declines with age and varies with body size. Younger adults often have CrCl around 90–140 mL/min. Because it is not normalized, interpreting it requires the individual's context. Drug-dosing ranges (e.g., &gt;50, 30–50, &lt;30 mL/min) are what matter for dosing.

❓ Should I use Cockcroft-Gault or CKD-EPI for drug dosing?

✅ Many drug labels still reference Cockcroft-Gault, so it remains clinically used. However, KDIGO 2024 recommends the race-free CKD-EPI equation for drug dosing when precision matters, and increasingly recommends eGFR-based dosing. Follow current institutional guidance.

❓ How do I convert creatinine from μmol/L to mg/dL?

✅ Divide by 88.4. The Cockcroft-Gault formula requires serum creatinine in mg/dL; if your lab reports μmol/L, convert before entering the value. A unit error changes the result by roughly 88×.

❓ Is this calculator for dosing medications?

✅ No. This is an educational tool that estimates creatinine clearance; it does not recommend specific drug doses. Medication dosing must be determined by a qualified healthcare professional applying the drug's approved criteria to the full clinical picture.