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.

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.