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Creatinine Clearance (Cockcroft-Gault) Practice

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Creatinine clearance estimates kidney function to guide renal dose adjustments. The Cockcroft-Gault equation is the pharmacy standard. The trickiest part is choosing the right body weight before plugging in.

FormulasCrCl = [(140 − age) × weight] ÷ (72 × SCr)  × 0.85 if femaleIBW (Devine) = 50 kg male or 45.5 kg female + 2.3 kg per inch over 5 feetIBW first → actual < IBW use actual; actual > 125% of IBW use AdjBW = IBW + 0.4(actual − IBW); otherwise IBW  •  some references use 120% or 130%, so follow the cutoff the question gives
Worked example

70-yr-old male, 5'10" (IBW = 73 kg), weighs 82 kg, SCr 1.2. Since 82 kg is between IBW and 125% of IBW (91.3 kg), use IBW. CrCl = (140 − 70) × 73 ÷ (72 × 1.2) = 59.1 mL/min.

Weight rule first, formula second. Using actual weight where AdjBW is required is the classic error.

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Creatinine Clearance
Calculate the creatinine clearance (Cockcroft-Gault) for a 69-year-old male, 5'7" tall, weighing 56 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.
mL/min

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How to set up a Cockcroft-Gault problem

Cockcroft-Gault estimates creatinine clearance from four things you can read off a chart: age, weight, sex and serum creatinine. It is the equation drug labeling and renal dosing tables are built on, which is why it is the one the NAPLEX tests. It is not the same as the eGFR your lab reports (that comes from CKD-EPI and is normalized to 1.73 m²), and the two numbers can differ enough to change a dose. When a question says "creatinine clearance" or "Cockcroft-Gault," use this and report mL/min.

CrCl (mL/min) = [(140 − age) × weight (kg)] ÷ (72 × SCr)  × 0.85 if female

The formula is easy. Almost every lost point comes from the weight you put into it. Do these three things in order.

1. Choose the weight before you touch the formula

Calculate ideal body weight first, every time, even when you suspect you won't use it:

Then compare the patient's actual weight to it.

The 125% cutoff is the one this site uses and the one most schools teach, but you will meet 120% and 130% in other references. When a question states a cutoff, use that one. When it doesn't, 125% is the safe default.

2. Serum creatinine goes in exactly as given

If the question gives SCr 0.6 mg/dL, 0.6 is the number in the denominator. Nothing is done to it first.

3. Apply the female factor last

Multiply by 0.85 after the division, not before, and not to the weight. The order doesn't change the arithmetic, but doing it last keeps it from being forgotten, which is the most common miss on this topic.

Worked example 1: the weight is IBW

A 65-year-old man, 5'10", weighs 78 kg, SCr 1.0 mg/dL.

IBW = 50 + 2.3 × 10 = 73 kg. 125% of IBW is 91.3 kg. Actual weight 78 kg is between 73 and 91.3, so use IBW.

CrCl = (140 − 65) × 73 ÷ (72 × 1.0) = 5,475 ÷ 72 = 76 mL/min

Worked example 2: adjusted body weight, female

A 58-year-old woman, 5'4", weighs 95 kg, SCr 1.2 mg/dL.

IBW = 45.5 + 2.3 × 4 = 54.7 kg. 125% of IBW is 68.4 kg. Actual weight 95 kg is above that, so use AdjBW.

AdjBW = 54.7 + 0.4 × (95 − 54.7) = 54.7 + 16.1 = 70.8 kg

Before the sex factor: (140 − 58) × 70.8 ÷ (72 × 1.2) = 5,806 ÷ 86.4 = 67.2

CrCl = 67.2 × 0.85 = 57.1 → 57 mL/min

Using her actual weight would give 77 mL/min. Using IBW would give 44. That spread is exactly why the weight step matters.

Worked example 3: underweight, elderly

An 84-year-old man, 5'8", weighs 58 kg, SCr 0.8 mg/dL.

IBW = 50 + 2.3 × 8 = 68.4 kg. Actual weight 58 kg is below IBW, so use actual weight.

CrCl = (140 − 84) × 58 ÷ (72 × 0.8) = 3,248 ÷ 57.6 = 56 mL/min

Where students lose the points

One thing worth knowing for practice

Drug labeling isn't always consistent with the rule above. The trials for the direct oral anticoagulants, for example, calculated Cockcroft-Gault with actual body weight, and some references recommend the same when dosing them. For an exam question, follow the question's instructions. At work, follow the labeling for the drug in front of you.

10 Creatinine Clearance (Cockcroft-Gault) practice problems with worked solutions

Every problem below is worked start to finish. Try it yourself first, then check the steps. For a fresh problem every time, use the practice box above. It generates unlimited variations of these same question types.

Problem 1: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 42-year-old female, 5'1" tall, weighing 73 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 74 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 1 inches = 47.8 kg.
  2. Choose the weight: Actual BW (73 kg) > 125% of IBW (59.75 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 47.8 + 0.4 × (73 − 47.8) = 57.88 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 42 yr) × 57.88 kg = 5672.24; denominator: 72 × 0.9 mg/dL = 64.8.
  5. 5672.24 ÷ 64.8 ≈ 87.5346; × 0.85 (female) ≈ 74.4 mL/min  (using AdjBW).
  6. Rounded as the question asks: 74 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 2: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 51-year-old female, 5'10" tall, weighing 73 kg, with a serum creatinine of 0.9 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 80 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 10 inches = 68.5 kg.
  2. Choose the weight: Actual BW (73 kg) is between IBW (68.5 kg) and 125% of IBW (85.63 kg) → use IBW = 68.5 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 51 yr) × 68.5 kg = 6096.5; denominator: 72 × 0.9 mg/dL = 64.8.
  5. 6096.5 ÷ 64.8 ≈ 94.0818; × 0.85 (female) ≈ 79.97 mL/min  (using IBW).
  6. Rounded as the question asks: 80 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 3: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 87-year-old female, 5'2" tall, weighing 82 kg, with a serum creatinine of 0.8 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 49 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 2 inches = 50.1 kg.
  2. Choose the weight: Actual BW (82 kg) > 125% of IBW (62.63 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 50.1 + 0.4 × (82 − 50.1) = 62.86 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 87 yr) × 62.86 kg = 3331.58; denominator: 72 × 0.8 mg/dL = 57.6.
  5. 3331.58 ÷ 57.6 ≈ 57.8399; × 0.85 (female) ≈ 49.16 mL/min  (using AdjBW).
  6. Rounded as the question asks: 49 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 4: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 82-year-old male, 5'5" tall, weighing 68 kg, with a serum creatinine of 2.6 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 19 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 5 inches = 61.5 kg.
  2. Choose the weight: Actual BW (68 kg) is between IBW (61.5 kg) and 125% of IBW (76.88 kg) → use IBW = 61.5 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 82 yr) × 61.5 kg = 3567; denominator: 72 × 2.6 mg/dL = 187.2.
  5. 3567 ÷ 187.2 ≈ 19.05 mL/min  (using IBW).
  6. Rounded as the question asks: 19 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 5: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 48-year-old female, 5'1" tall, weighing 65 kg, with a serum creatinine of 0.8 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 74 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 1 inches = 47.8 kg.
  2. Choose the weight: Actual BW (65 kg) > 125% of IBW (59.75 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 47.8 + 0.4 × (65 − 47.8) = 54.68 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 48 yr) × 54.68 kg = 5030.56; denominator: 72 × 0.8 mg/dL = 57.6.
  5. 5030.56 ÷ 57.6 ≈ 87.3361; × 0.85 (female) ≈ 74.24 mL/min  (using AdjBW).
  6. Rounded as the question asks: 74 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 6: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 65-year-old male, 5'7" tall, weighing 78 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 31 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 7 inches = 66.1 kg.
  2. Choose the weight: Actual BW (78 kg) is between IBW (66.1 kg) and 125% of IBW (82.63 kg) → use IBW = 66.1 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 65 yr) × 66.1 kg = 4957.5; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4957.5 ÷ 158.4 ≈ 31.3 mL/min  (using IBW).
  6. Rounded as the question asks: 31 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 7: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 45-year-old female, 5'3" tall, weighing 46 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 23 mL/min

Solution
  1. IBW (female): 45.5 + 2.3 × (inches over 60) = 45.5 kg + 2.3 kg/inch × 3 inches = 52.4 kg.
  2. Choose the weight: Actual BW (46 kg) < IBW (52.4 kg) → patient is underweight → use actual BW = 46 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr) × 0.85 (female).
  4. Numerator: (140 − 45 yr) × 46 kg = 4370; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4370 ÷ 158.4 ≈ 27.5884; × 0.85 (female) ≈ 23.45 mL/min  (using actual BW).
  6. Rounded as the question asks: 23 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 8: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 61-year-old male, 6'1" tall, weighing 125 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 49 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 13 inches = 79.9 kg.
  2. Choose the weight: Actual BW (125 kg) > 125% of IBW (99.88 kg) → patient is obese → AdjBW = IBW + 0.4 × (actual − IBW) = 79.9 + 0.4 × (125 − 79.9) = 97.94 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 61 yr) × 97.94 kg = 7737.26; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 7737.26 ÷ 158.4 ≈ 48.85 mL/min  (using AdjBW).
  6. Rounded as the question asks: 49 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 9: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 43-year-old male, 5'9" tall, weighing 57 kg, with a serum creatinine of 1.0 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 77 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 9 inches = 70.7 kg.
  2. Choose the weight: Actual BW (57 kg) < IBW (70.7 kg) → patient is underweight → use actual BW = 57 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 43 yr) × 57 kg = 5529; denominator: 72 × 1.0 mg/dL = 72.
  5. 5529 ÷ 72 ≈ 76.79 mL/min  (using actual BW).
  6. Rounded as the question asks: 77 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Problem 10: Creatinine Clearance

Calculate the creatinine clearance (Cockcroft-Gault) for a 88-year-old male, 6'0" tall, weighing 91 kg, with a serum creatinine of 2.2 mg/dL. Select the appropriate body weight: use actual body weight if it is below IBW, adjusted body weight if it exceeds 125% of IBW, and IBW otherwise. Round your answer to the nearest whole number.

Answer 25 mL/min

Solution
  1. IBW (male): 50 + 2.3 × (inches over 60) = 50 kg + 2.3 kg/inch × 12 inches = 77.6 kg.
  2. Choose the weight: Actual BW (91 kg) is between IBW (77.6 kg) and 125% of IBW (97 kg) → use IBW = 77.6 kg.
  3. Cockcroft-Gault: CrCl = [(140 − age) × wt] ÷ (72 × SCr).
  4. Numerator: (140 − 88 yr) × 77.6 kg = 4035.2; denominator: 72 × 2.2 mg/dL = 158.4.
  5. 4035.2 ÷ 158.4 ≈ 25.47 mL/min  (using IBW).
  6. Rounded as the question asks: 25 mL/min.

The weight-selection algorithm: always calculate IBW first. Underweight (actual < IBW) → use actual body weight. Obese (actual > 125% of IBW) → use AdjBW = IBW + 0.4(actual − IBW). Otherwise → use IBW.

Sources and how far they go

Where a convention on this page comes from a published standard, the standard is named. Where it comes from a textbook or from ordinary practice instead, the entry says so. That difference matters when a preceptor or an exam disagrees with you.

Citations are to the source of the method. They are not a review of this page, and none of these bodies has reviewed or endorsed it.

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