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Walk-through

How to Use This Calculator

3 steps

1

Enter age, sex, weight and creatinine

Type the patient's age and weight, choose sex, and enter the serum creatinine from a recent lab result. Use the unit toggles to switch weight between kg and lb and creatinine between mg/dL (conventional, US) and µmol/L (SI). The calculator converts everything to the units Cockcroft-Gault expects before computing.

2

Choose a weight basis

Pick actual, ideal, or adjusted body weight. Actual weight is the default. For ideal (Devine) and adjusted weight the calculator needs height, so enter it too. In obesity, actual body weight inflates the estimate, so many clinicians use ideal or adjusted weight for renal drug dosing.

3

Read the clearance and stage

The headline shows creatinine clearance in mL/min and the kidney-function band it falls in. The interpretation panel explains what that means for drug dosing. Open the Weight Basis tab to compare all three weight bases side by side, and the Function Stages tab for the reference ranges.

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Reference

Formula & Methodology

4 formulas

Cockcroft-Gault creatinine clearance

CrCl (mL/min) = ((140 − age) × weight_kg × sexFactor) / (72 × SCr_mg/dL)

The 1976 equation. sexFactor is 0.85 for women and 1 for men, reflecting lower average muscle mass. Age is in years, weight in kilograms, and serum creatinine (SCr) in mg/dL. It estimates clearance in millilitres per minute.

SI creatinine conversion

SCr_mg/dL = SCr_µmol/L ÷ 88.42

Labs outside the US usually report creatinine in µmol/L. Divide by 88.42 (equivalently multiply by ≈ 0.0113) to get mg/dL before applying Cockcroft-Gault. The calculator does this automatically when you pick the µmol/L unit.

Devine ideal body weight (IBW)

Men: 50 + 2.3 × (height_in − 60) · Women: 45.5 + 2.3 × (height_in − 60)

Ideal body weight in kilograms from height in inches over 5 feet (60 in). Used as the weight basis when actual weight would overestimate clearance, and as the starting point for adjusted body weight.

Adjusted body weight (AdjBW)

AdjBW = IBW + 0.4 × (actual_kg − IBW)

A common correction in obesity (actual weight above IBW). It adds 40% of the excess over ideal weight, partly accounting for the larger lean mass in heavier people without using full actual weight.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Editorial Review · Updated 2026-06-13 · 3 sources

Editorial accountability

Author: {{^authorProfileUrl}}Calculover Editorial Team{{/authorProfileUrl}} - Editor

Owner: Calculover Editorial Team - Editorial owner

Reviewer: Calculover Editorial Review - Clinical-source review

Last reviewed: 2026-06-13

Last verified: 2026-06-13

Data effective: 2026-06-13

Methodology

The Creatinine Clearance Calculator applies the Cockcroft-Gault equation (Cockcroft & Gault, Nephron 1976) to the age, sex, body weight, and serum creatinine entered by the user. Serum creatinine in SI units (µmol/L) is converted to mg/dL by dividing by 88.42 before use. Ideal body weight uses the Devine formula and adjusted body weight uses ideal body weight plus 40% of the excess of actual over ideal weight. All constants (the 140 intercept, the 72 denominator, the 0.85 female factor) are taken directly from the original equation. The kidney-function bands shown for interpretation borrow the KDIGO GFR categories and are labelled as a drug-dosing reference, not a chronic-kidney-disease staging tool.

Assumption: Serum creatinine is at steady state, from a recent lab result, and entered in the selected unit.

Assumption: The patient is an adult with typical body composition; the relationship between creatinine and muscle mass underlying the equation holds.

Assumption: The user wants a reference creatinine clearance estimate, not an individualized medication dose, diagnosis, or treatment plan.

Limitations & guidance

Cockcroft-Gault is unreliable when kidney function is changing rapidly (acute kidney injury), in pregnancy, in amputees or people with very atypical body composition, and outside the adult age range it was validated in.

Creatinine clearance (mL/min) is not normalised to body surface area and is not interchangeable with eGFR (mL/min/1.73 m²); eGFR is preferred for staging chronic kidney disease.

This tool does not determine, verify, or adjust any medication dose. Renal dosing in practice also depends on drug-specific cutoffs, caps, rounding, and clinical judgement that this calculator does not model.

Professional guidance: The Creatinine Clearance Calculator is for health education and calculation transparency only. It is an estimate for reference, not a substitute for clinical judgement, and it is not medical advice, diagnosis, treatment, dosing guidance, or a substitute for care from a licensed healthcare professional.

Primary sources

Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41. - Nephron (Karger)

Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650-655 (ideal body weight formula). - Drug Intelligence & Clinical Pharmacy

Inker LA, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race (CKD-EPI 2021). - New England Journal of Medicine

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Glossary

Key Terms Explained

8 terms

Creatinine clearance (CrCl) The volume of blood cleared of creatinine per minute (mL/min), used as an estimate of kidney filtration. The Cockcroft-Gault value is the reference most drug labels use for renal dose adjustment.

Cockcroft-Gault equation A 1976 formula that estimates creatinine clearance from age, sex, body weight, and serum creatinine. Simple and durable, it remains the standard for renal drug dosing.

Serum creatinine (SCr) A waste product of muscle metabolism cleared by the kidneys. Higher serum creatinine means lower clearance. Reported in mg/dL (US) or µmol/L (SI).

eGFR Estimated glomerular filtration rate, usually from the CKD-EPI equation and reported per 1.73 m² body surface area. eGFR is preferred for staging chronic kidney disease; CrCl is preferred for drug dosing.

Ideal body weight (IBW) A height-based reference weight (Devine formula). Using IBW in Cockcroft-Gault avoids the overestimate that actual body weight produces in obesity.

Adjusted body weight (AdjBW) Ideal body weight plus 40% of the excess of actual over ideal weight. A middle-ground weight basis often used for renal dosing in obese patients.

mL/min vs mL/min/1.73 m² Cockcroft-Gault CrCl is an absolute clearance in mL/min. eGFR is normalised to a standard 1.73 m² body surface area. The two are not interchangeable, especially at the extremes of body size.

Renal dose adjustment Changing a drug's dose or interval because reduced kidney clearance would otherwise let it accumulate. Many drug labels give the cutoffs in terms of Cockcroft-Gault creatinine clearance.

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Scenarios

Real-World Examples

3 worked examples

RG

Robert, 78 — older adult on multiple medications

Elderly, mild impairment

Age 78 years Sex Male Weight 72 kg Serum creatinine 1.3 mg/dL CrCl ≈ 53 mL/min

Robert's creatinine clearance is about 53 mL/min — moderately decreased — even though his creatinine of 1.3 mg/dL looks only mildly raised. This is the classic reason Cockcroft-Gault matters in older adults: age and lower muscle mass pull clearance down faster than creatinine alone suggests, so several renally-cleared drugs may need a reduced dose.

AN

Ana, 28 — healthy young woman

Young adult, normal function

Age 28 years Sex Female Weight 62 kg Serum creatinine 0.8 mg/dL CrCl ≈ 102 mL/min

Ana's clearance is about 102 mL/min — normal. The 0.85 female factor is already applied. For most drugs no renal adjustment is needed at this level, though a handful of agents still specify checks regardless of clearance.

MK

Marcus, 58 — obese patient, dosing decision

Why weight basis matters

Age 58 years Sex Male Weight 118 kg (height 178 cm) Serum creatinine 1.0 mg/dL CrCl (actual vs adjusted) ≈ 134 vs ≈ 104 mL/min

With actual body weight Marcus's clearance computes to about 134 mL/min, but his ideal body weight is roughly 73 kg, so using actual weight overestimates clearance. Switching to adjusted body weight gives about 104 mL/min (ideal weight gives about 83) — a large spread that could change whether a renally-cleared drug is dosed normally or reduced. In obesity, many clinicians use ideal or adjusted weight; follow the specific drug's guidance.

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Deep Dive

Creatinine Clearance and the Cockcroft-Gault Equation

4 chapters · 6 min read

Creatinine clearance is one of the oldest and most clinically durable kidney estimates. Despite newer equations, the Cockcroft-Gault formula remains the reference for adjusting drug doses to kidney function — which is why understanding how it is calculated, when to use it, and how the weight basis changes the answer is so useful. This guide covers what creatinine clearance is, why CrCl and eGFR are not the same thing, and how to read the result responsibly.

What creatinine clearance estimates

Creatinine is a waste product of muscle metabolism produced at a fairly steady rate and removed by the kidneys. Because production is roughly constant for a given person, the blood level of creatinine reflects how well the kidneys are clearing it: as filtration falls, creatinine rises. Creatinine clearance turns that relationship into a number — the millilitres of blood cleared of creatinine each minute — that approximates the glomerular filtration rate.

The Cockcroft-Gault equation, published by Donald Cockcroft and Henry Gault in 1976, estimates clearance from four readily available inputs: age, sex, body weight, and serum creatinine. It builds in the fact that creatinine production declines with age and is lower on average in women (the 0.85 factor) and in people with less muscle. That makes it more informative than serum creatinine alone, which can look reassuringly normal in a frail older adult whose true clearance is substantially reduced.

CrCl versus eGFR — why both still exist

Modern labs usually report an estimated glomerular filtration rate (eGFR), most often from the 2021 race-free CKD-EPI creatinine equation, normalised to a standard body surface area of 1.73 m² and expressed as mL/min/1.73 m². eGFR is the preferred tool for detecting and staging chronic kidney disease, and it is what nephrology guidelines use.

So why does Cockcroft-Gault creatinine clearance persist? Because most drug dosing studies and FDA drug labels were written using Cockcroft-Gault, and the renal-adjustment cutoffs they specify are defined in those terms. Creatinine clearance is also an absolute clearance in mL/min — not normalised to body surface area — which is what actually governs how fast a drug leaves the body of a specific person. For routine renal drug dosing, then, Cockcroft-Gault CrCl remains the reference, even though eGFR is preferred for staging kidney disease. The two numbers usually move together but are not interchangeable, especially at very high or very low body size.

Why the weight basis changes the answer

Cockcroft-Gault multiplies by body weight, so the weight you enter scales the result directly. In a person near their ideal weight this rarely matters. In obesity it matters a great deal: creatinine is produced mainly by lean tissue, but fat mass adds to total body weight without adding much creatinine clearance. Plugging full actual weight into the equation therefore overestimates clearance, sometimes substantially.

To handle this, clinicians choose a weight basis. Ideal body weight (the Devine formula) uses height alone and avoids the obesity overestimate, but can underestimate clearance in muscular patients. Adjusted body weight adds 40% of the excess over ideal weight back in, splitting the difference, and is a common choice for renal dosing in obese patients. This calculator computes all three so you can see the spread; which one to use depends on the drug, the clinical context, and institutional guidance.

Reading the result responsibly

Cockcroft-Gault is an estimate built on assumptions: a steady-state serum creatinine, adult physiology, and a relationship between creatinine and muscle mass that holds for most but not all people. It is unreliable when kidney function is changing rapidly (acute kidney injury), in pregnancy, in amputees or people with very atypical body composition, and outside the adult age range it was validated in. A single value is a snapshot, not a diagnosis.

Use the number the way a clinician does: as a starting point that is then weighed against the specific drug's label, the patient's trajectory, and clinical judgement. This calculator is a transparency and education tool. It does not determine, verify, or adjust any medication dose, and it is not a substitute for care from a qualified healthcare professional.

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Questions

Frequently Asked Questions

7 questions

What is a normal creatinine clearance?+

A healthy young adult typically has a creatinine clearance around 90–120 mL/min or higher. Values fall gradually with age. Below about 60 mL/min indicates moderately reduced filtration, and below 30 mL/min indicates severe reduction. These bands are a guide — interpret any single value in clinical context, not as a diagnosis.

Should I use creatinine clearance or eGFR for drug dosing?+

Most drug labels define renal dose adjustments using Cockcroft-Gault creatinine clearance, so CrCl is the reference for dosing. eGFR (CKD-EPI) is preferred for detecting and staging chronic kidney disease. They usually agree closely but are not interchangeable, especially at very high or low body size, because eGFR is normalised to 1.73 m² body surface area and CrCl is not.

Which body weight should I enter?+

Start with actual body weight. In obesity, actual weight overestimates clearance because fat adds weight without adding much filtration, so many clinicians switch to ideal (Devine) or adjusted body weight for renal dosing. The Weight Basis tab shows all three so you can compare; follow the specific drug's guidance and your institution's policy.

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

Divide the µmol/L value by 88.42 (or multiply by about 0.0113) to get mg/dL. For example, 97 µmol/L ≈ 1.1 mg/dL. The calculator does this automatically — just choose the µmol/L unit and enter your lab's value.

Why does sex change the result?+

The Cockcroft-Gault equation multiplies by 0.85 for women, reflecting lower average muscle mass and therefore lower creatinine production for the same body weight. For otherwise identical inputs, the female estimate is 85% of the male estimate.

Is this calculator accurate enough to dose medication?+

No — it is for reference and education only. It computes the Cockcroft-Gault estimate transparently, but it does not account for acute changes in kidney function, dose caps, rounding rules, drug-specific cutoffs, or other clinical factors. Never make a medication decision from this tool; confirm dosing with a qualified clinician and the drug's authoritative labelling.

Can I use this for children?+

No. Cockcroft-Gault was developed and validated in adults. Paediatric kidney function is estimated with different equations (such as the bedside Schwartz formula). The calculator warns when the age entered is outside the adult range.

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CrCl (mL/min)	Kidney function	General dosing context
≥ 90	Normal or high	Standard dosing for most drugs unless a label specifies otherwise.
60–89	Mildly decreased	Most drugs unchanged; check renally-cleared agents.
30–59	Moderately decreased	Many renally-cleared drugs require dose reduction.
15–29	Severely decreased	Large reductions common; some drugs contraindicated.
< 15	Kidney failure	Specialist input; many agents avoided or heavily adjusted.

Creatinine Clearance Calculator