Creatinine Clearance Calculator (CrCl)

Use the Creatinine Clearance Calculator (CrCl)

Estimate creatinine clearance in mL/min using Cockcroft–Gault. Enter age, sex, weight, and serum creatinine; switch units freely.

How to Use Creatinine Clearance Calculator (CrCl)

1. Step 1: Enter age and sex

   Add your age in years and select male or female.

2. Step 2: Add weight and units

   Enter weight (kg or lb). Optionally enter height to enable IBW/Adjusted and BSA.

3. Step 3: Pick weight method

   Choose Actual, Ideal (IBW), or Adjusted weight depending on body size.

4. Step 4: Enter serum creatinine

   Input creatinine in mg/dL or µmol/L; the tool converts automatically.

5. Step 5: Review CrCl and notes

   View mL/min result, optional 1.73 m² value, and classification context.

Key Features

• Cockcroft–Gault CrCl
• mg/dL ↔ µmol/L auto‑convert
• Actual/Ideal/Adjusted weight
• Optional BSA normalization
• Mobile‑first UI
• Copy/share result

Understanding Results

Creatinine clearance formula (Cockcroft–Gault)

Cockcroft–Gault estimates creatinine clearance (CrCl) as:
CrCl (mL/min) = [(140 − age) × weight (kg)] ÷ [72 × serum creatinine (mg/dL)]. For women, multiply by 0.85. Our tool converts µmol/L to mg/dL when needed and lets you choose Actual, Ideal (IBW), or Adjusted body weight.

Reference Ranges & Interpretation

As a broad guide for adults: ≥90 mL/min is generally consistent with normal kidney filtration; 60–89 suggests a mild decrease; 30–59 a moderate decrease; 15–29 severe; and <15 mL/min is typically in the kidney failure range. Use these bands as orientation only—clinical context and trends matter more than a single number.

Assumptions & Limitations

Cockcroft–Gault is a population‑based estimate. Results can be less reliable during acute illness, dehydration, pregnancy, extremes of body size or muscle mass, and in rapidly changing kidney function. It is commonly used to guide drug dosing but does not diagnose disease. Confirm important decisions with a clinician.

Complete Guide: Creatinine Clearance Calculator (CrCl)

Estimate clearance using Cockcroft-Gault with our creatinine clearance calculator (CrCl calculator). Input weight, sex, and age for accurate dosing context.

The creatinine clearance calculator uses the Cockcroft–Gault equation to estimate kidney filtration in milliliters per minute (mL/min). It is widely used to guide drug dosing, especially for medicines cleared by the kidneys. The estimate is convenient and fast, yet it is still an approximation. Your lab’s eGFR (usually normalized to a body surface area of 1.73 m²) may not match your Cockcroft–Gault result exactly due to different equations and normalizations. The sections below explain what each input means, when to use alternative weights, and how to read your result with context.

What is creatinine clearance?

Creatinine clearance (CrCl) is a practical estimate of how quickly your kidneys clear creatinine from your blood. Creatinine is a waste product of muscle metabolism. When kidney function is lower, creatinine tends to build up and the serum creatinine value rises. Cockcroft–Gault combines age, sex, weight, and serum creatinine into a single number that approximates the kidney’s filtering capacity, expressed as mL/min. Clinicians have used it for decades to adjust doses for many medications that are renally eliminated.

Importantly, CrCl is an estimate based on population data. It is not a direct measurement like a timed urine clearance study, and it does not replace clinical judgment. Hydration status, muscle mass, acute illness, and lab variability can all nudge results up or down.

Think of the number as a snapshot of filtration at a point in time. If your creatinine or hydration changes substantially from day to day, the estimate will track that movement, too. For that reason, professionals often look at prior results and the bigger clinical picture, rather than relying on a single reading in isolation.

Cockcroft–Gault formula explained

The Cockcroft–Gault equation estimates creatinine clearance using the following relationship:

CrCl (mL/min) = [(140 − age) × weight (kg)] ÷ [72 × serum creatinine (mg/dL)]. For women, multiply the result by 0.85. The idea is that younger age and lower serum creatinine generally indicate stronger kidney filtering, while higher weight correlates with a larger distribution space and creatinine production. Because the formula expects creatinine in mg/dL, our tool automatically converts from µmol/L when needed.

Our calculator also offers an optional normalization to 1.73 m² using the Mosteller body surface area (BSA) formula. Some labs report eGFR normalized to 1.73 m², so showing a normalized CrCl helps you compare numbers cautiously. Keep in mind that Cockcroft–Gault was not originally defined to be normalized, and drug dosing references typically use the non‑normalized value.

Why does the equation use 140 − age? It reflects the observation that kidney function tends to decline gradually with age in many adults. The sex adjustment (×0.85 for women) attempts to account for lower average muscle mass and creatinine generation. These adjustments are blunt instruments: individual people vary widely, which is why estimates are best interpreted alongside clinical context.

Choosing Actual vs IBW vs Adjusted body weight

Weight selection can meaningfully change the result. The calculator supports three options:

• Actual body weight (ABW): Your current weight. This is straightforward and commonly used.
• Ideal body weight (IBW): Estimated from height and sex using the Devine formula. IBW reduces the influence of excess body fat on the calculation.
• Adjusted body weight (AdjBW): IBW + 0.4 × (ABW − IBW). Some clinicians use AdjBW when ABW is substantially above IBW (for example, ≥120%).

If you are unsure which approach to use, a reasonable starting point is Actual body weight. If you have a much higher weight compared with IBW, consider Adjusted body weight and discuss with your clinician or pharmacist. You can estimate IBW separately with our ideal body weight calculator and compare to your actual weight. For context on total mass and composition, you can also check your adult BMI and lean body mass.

Why does weight matter? Creatinine is produced by muscle tissue. People with higher body mass often produce more creatinine; those with lower muscle mass (for example, frail older adults) produce less. Using IBW or Adjusted weight can soften extremes and may align estimates better with practical dosing targets in certain scenarios.

Units and conversions

Labs may report serum creatinine in mg/dL or µmol/L. The conversion is 1 mg/dL ≈ 88.4 µmol/L. Our calculator detects the selected unit and performs the conversion internally so that the equation always uses mg/dL. For height and weight, you can switch between centimeters/inches and kilograms/pounds; the calculation handles the conversions seamlessly.

If you want to compare a BSA‑normalized CrCl with an eGFR reported at 1.73 m², enable height to compute BSA (Mosteller) and review the “normalized to 1.73 m²” line in the results. If you specifically need body surface area for other purposes, you can also use our dedicated BSA calculator.

For the best experience: double‑check the units printed on your lab report, enter values carefully using the correct unit toggles, and consider computing both Actual and Adjusted weight results if you are significantly above IBW. If both values lead to the same dosing bracket, you gain confidence. If they straddle a threshold, that is a signal to review trends and select the safer plan with a professional.

Interpreting your result

Creatinine clearance is expressed in mL/min. As a rough guide, values above ~90 mL/min are generally consistent with normal adult kidney function; 60–89 suggests a mild reduction; 30–59 indicates a moderate decrease; 15–29 is severe; and <15 mL/min is typically in the kidney failure range. These tiers align with common eGFR staging bands, although Cockcroft–Gault is not an eGFR. Real clinical decisions consider more than a single estimate: protein in the urine, trends over time, hydration, medications, and individual context.

Use caution at the extremes of age, muscle mass, and body size. Elderly people with low muscle mass may have “normal‑looking” creatinine but reduced kidney function. Conversely, muscular individuals can have higher creatinine without kidney disease. This is why the equation includes age, sex, and weight—to partially account for these differences—but no equation is perfect.

Consider, too, the timing of your lab draw. Creatinine can change with hydration, recent strenuous exercise, and certain medications. If your value seems unusual for you, repeating a lab on another day can be helpful before making large decisions.

CrCl vs eGFR — why they differ

eGFR is an estimate of kidney filtration derived from other equations (such as CKD‑EPI), typically normalized to a standard body surface area of 1.73 m². Cockcroft–Gault (CrCl) is not normalized by default and was historically used for drug dosing studies. Because of these origins, dosing recommendations are often still written in terms of CrCl bands, whereas CKD staging and lab reports rely on eGFR.

The two numbers can be close but are not interchangeable. Differences are expected, particularly if your body size differs significantly from the “average” assumptions or if creatinine measurement methods vary. Our tool shows both the non‑normalized CrCl (primary for dosing) and an optional 1.73 m²‑normalized value to facilitate careful side‑by‑side review.

For a high‑level review of kidney health concepts, see our kidney function calculator which covers eGFR context and staging.

Medication dosing and practical notes

Many common medications list dosing adjustments by creatinine clearance brackets (for example, reduce dose when CrCl < 50 mL/min, or avoid altogether if CrCl < 30). Pharmacists and clinicians usually round inputs sensibly and consider recent changes in kidney function. If your value sits near a threshold, trends and clinical context matter; the safer adjustment is often chosen until more information is available.

• Use recent labs. Large shifts in creatinine over hours or days can make any estimate unreliable.
• Confirm units. A common source of error is mixing mg/dL and µmol/L.
• Choose a weight method appropriate to body size; consider Adjusted weight if ABW is far above IBW.
• Look for consistency with other data: urine output, hydration status, electrolytes, and overall clinical picture.

When two methods give you similar numbers, confidence improves. When they disagree, use the discrepancy as a cue to slow down: verify inputs, re‑check past values, and consider the more conservative dosing plan until more information is available.

It also helps to write down a short summary for your clinician or pharmacist: the value you entered for each field, the unit, and the resulting CrCl. Our calculator includes a one‑tap copy button to make this easy on mobile—handy when discussing options during a visit or telehealth call.

If you are actively optimizing dosing under professional guidance, body size metrics can provide context: IBW from the IBW calculator, overall size from BSA, and weight classification from the BMI calculator can help frame dosing choices.

Limitations and special cases

Cockcroft–Gault is convenient, but it has limitations. It was derived from a modest number of adults in the 1970s and assumes relatively steady creatinine production and stable kidney function. Situations where caution is warranted include acute kidney injury, severe liver disease, pregnancy, very low or very high muscle mass, extremes of age, amputations, and conditions that alter creatinine handling. In such scenarios, clinicians may use alternative equations, timed urine collections, or cystatin C–based estimates to cross‑check results.

Using IBW or Adjusted weight can mitigate over‑ or under‑estimation for people at the extremes of body size, but it does not eliminate all bias. When results drive important dosing decisions, a clinical professional should interpret them in context.

Another special consideration is rapidly changing kidney function, such as in serious infections, heart failure exacerbations, or immediately after starting or stopping certain medications. In these windows, creatinine may lag actual filtration capacity, and day‑to‑day values can diverge. Repeating labs and combining information from urine output and the overall clinical picture provide a steadier compass than any single equation.

Finally, be mindful that laboratory measurement techniques can vary slightly between facilities. If you are tracking a trend over time, it is ideal (when practical) to use the same lab and similar timing conditions—well‑hydrated, not immediately after intense exercise—to minimize noise.

Worked examples

Example 1: A 65‑year‑old man, 70 kg, 170 cm, serum creatinine 1.0 mg/dL. Using Actual body weight, CrCl ≈ [(140 − 65) × 70] ÷ (72 × 1.0) ≈ (75 × 70) ÷ 72 ≈ 72.9 mL/min. Using IBW (≈ 66 kg for 170 cm) would yield a slightly lower value; Adjusted (if applicable) would sit between the two. In most dosing tables, this falls in a moderate range where standard dosing may still apply, but some drugs begin to adjust below 60 mL/min.

Example 2: A 75‑year‑old woman, 90 kg, 160 cm, serum creatinine 1.3 mg/dL. Actual body weight gives CrCl ≈ [(140 − 75) × 90 × 0.85] ÷ (72 × 1.3). That is (65 × 90 × 0.85) ÷ 93.6 ≈ 52.9 mL/min. IBW for 160 cm (≈ 52 kg) produces a much lower value, while Adjusted weight sits between Actual and IBW. If Actual is much higher than IBW, many clinicians will look closely at the Adjusted result when selecting doses.

Example 3: A very muscular 40‑year‑old man, 95 kg, 180 cm, serum creatinine 1.4 mg/dL after an intense gym session. Creatinine may be transiently elevated from exercise and muscle mass; Cockcroft–Gault will produce a relatively low clearance in this snapshot. Repeating labs at rest and confirming hydration can avoid over‑interpreting a single low reading in an otherwise healthy person.

These scenarios illustrate how the same equation can yield very different values depending on biologic inputs. Rather than memorizing the numbers, learn the workflow: confirm units, choose a sensible weight method, compute, and then read the result against a short list of dosing thresholds for the specific medication.

Quick answers (mini‑FAQ)

Is Cockcroft–Gault the same as eGFR? No. They are different equations with different goals. CrCl (Cockcroft–Gault) is commonly used for drug dosing; eGFR is used for staging and general kidney health reporting.

Should I normalize CrCl to 1.73 m²? Drug labels typically reference non‑normalized CrCl. Normalizing can help compare with eGFR, but dosing usually follows the non‑normalized figure.

Which weight should I choose? Actual weight is a reasonable default. If ABW is much higher than IBW, many clinicians consider Adjusted weight. You can compute IBW with our IBW calculator.

Will dehydration change results? Yes. Dehydration and acute illness can shift creatinine quickly, making any single estimate less reliable. Use recent labs and trends.

Where can I learn more? See reputable clinical pharmacotherapy references and national kidney organizations for detailed dosing guidance and CKD staging concepts.

Frequently Asked Questions