Creatinine Clearance Calculator
Cockcroft-Gault creatinine clearance on actual, ideal and adjusted body weight, with why drug labels still use it rather than the CKD-EPI eGFR.
Creatinine Clearance Calculator: with the default inputs, creatinine clearance is 85.
From a standard blood panel. Set the units below to match the report.
Only needed for the ideal and adjusted body weight versions.
mL/min.
- On actual body weight
- 85
- On ideal body weight
- 74
- On adjusted body weight
- 78
- Weight used
- 81.6 kg
- CKD-EPI 2021 eGFR for comparison
- 84mL/min/1.73 m² — a different quantity, not a rival estimate of the same one.
- Which weight the labelling rule points to
- Actual weight is 15.5% above ideal, below the 25% trigger, so total body weight applies
- Creatinine in mg/dL
- 1
Assumptions
- This is an estimate for education. It does not diagnose anything and does not replace clinical judgement. It is not a prescribing tool.
- Cockcroft-Gault as written into FDA-approved labelling: (140 − age) × weight in kg ÷ (72 × creatinine in mg/dL), × 0.85 for women.
- Creatinine converts at 1 mg/dL = 88.4 µmol/L.
- Ideal body weight uses Devine's equation and adjusted body weight adds 0.4 of the excess over ideal; the default descriptor follows the 25%-over rule in FDA-approved plazomicin labelling.
- The CKD-EPI 2021 figure shown alongside is a different quantity — indexed to 1.73 m² — and is context, not a check.
- The equation assumes a stable creatinine and was derived in adults aged 18 to 92 before creatinine assays were standardised to the current reference method.
| Weight descriptor | Weight (kg) | CrCl (mL/min) | |
|---|---|---|---|
| Actual body weight | 81.6 | 85 | ← headline |
| Ideal body weight (Devine) | 70.7 | 74 | |
| Adjusted body weight | 75.1 | 78 |
Cockcroft-Gault is linear in weight, so the descriptor you choose scales the answer directly. In an obese patient the actual-weight version can be half as large again as the adjusted-weight version.
How this is worked out
The formula
Cockcroft-Gault, creatinine clearance in mL/min: CrCl = (140 − age) × weight (kg) ÷ (72 × serum creatinine in mg/dL) females: multiply by 0.85 age in years; µmol/L → mg/dL: divide by 88.4 Weight descriptors: ideal (Devine) = 50 kg (men) or 45.5 kg (women) + 2.3 kg per inch over 5 feet adjusted = ideal + 0.4 × (actual − ideal)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Serum creatinine
- From a standard blood panel. Set the units below to match the report.from 0 to 2000 · defaults to 1
- Creatinine units
- Choose one of 2 options.mg/dL (United States) · µmol/L (most other countries)
- Age
- A number.from 18 to 120 · whole numbers only · defaults to 65
- Sex
- Choose one of 2 options.Male · Female — multiply by 0.85
- Actual body weight
- A number.in lb, kg, st · from 20 to 800 · defaults to 180
- Height
- Only needed for the ideal and adjusted body weight versions.in in, cm, m, ft · from 36 to 96 · defaults to 69
- Weight used in the equation(under More options)
- All four are shown either way; this picks the headline number.Follow the FDA labelling rule (adjusted if 25% or more over ideal) · Actual body weight · Ideal body weight (Devine) · Adjusted body weight
What you get back
- Creatinine clearancemain answer
- mL/min.
- On actual body weight
- On ideal body weight
- On adjusted body weight
- Weight used
- CKD-EPI 2021 eGFR for comparison
- mL/min/1.73 m² — a different quantity, not a rival estimate of the same one.
- Which weight the labelling rule points to
- Creatinine in mg/dL
What this assumes
- This is an estimate for education. It does not diagnose anything and does not replace clinical judgement. It is not a prescribing tool.
- Cockcroft-Gault as written into FDA-approved labelling: (140 − age) × weight in kg ÷ (72 × creatinine in mg/dL), × 0.85 for women.
- Creatinine converts at 1 mg/dL = 88.4 µmol/L.
- Ideal body weight uses Devine's equation and adjusted body weight adds 0.4 of the excess over ideal; the default descriptor follows the 25%-over rule in FDA-approved plazomicin labelling.
- The CKD-EPI 2021 figure shown alongside is a different quantity — indexed to 1.73 m² — and is context, not a check.
- The equation assumes a stable creatinine and was derived in adults aged 18 to 92 before creatinine assays were standardised to the current reference method.
About this calculator
This is an estimate for education. It does not diagnose anything and does not replace clinical judgement. It is not a prescribing tool.
Why a 1976 equation is still here
Cockcroft and Gault published their equation in Nephron in 1976, fitted to 249 patients aged 18 to 92. It is old, it is imprecise, and it is still the equation most drug labels tell you to use. That is not inertia alone. Almost every renal dose adjustment in FDA-approved labelling was derived from studies that estimated renal function with Cockcroft-Gault, so the thresholds in those labels — reduce the dose below 50 mL/min, avoid below 30 — are calibrated to what this equation reports. Substituting a different estimate changes what the threshold means.
How it differs from the eGFR on your lab report
This is the distinction that causes the most confusion, and it is not a matter of one being better.
They are different quantities. Cockcroft-Gault estimates creatinine clearance in mL/min, for the actual person: a bigger person clears more, and the number reflects that. The CKD-EPI 2021 equation on your lab report estimates glomerular filtration rate in mL/min per 1.73 m² — normalised to a standard body surface area so that populations can be compared and staged. For someone close to average size the two land near each other. For someone much larger or smaller they do not, and neither is wrong.
They measure slightly different things. Creatinine is secreted by the renal tubules as well as filtered, so creatinine clearance runs above true GFR. Cockcroft-Gault was fitted against measured creatinine clearance, so it inherits that overestimate. CKD-EPI was fitted against measured GFR.
They are used for different jobs. CKD-EPI is the equation for staging chronic kidney disease under KDIGO and is what laboratories report. Cockcroft-Gault is the equation most drug labelling specifies for dose adjustment. FDA guidance accepts either a contemporary eGFR equation or Cockcroft-Gault for renal dosing studies, but adds an important detail: when a dosing recommendation uses eGFR, it should be expressed in mL/min rather than indexed to 1.73 m², by multiplying by the patient's own body surface area and dividing by 1.73. The CKD-EPI figure shown here for comparison is the indexed one, which is why it should be read as context and not as a check.
The weight question
Cockcroft-Gault is linear in weight, so which weight you feed it scales the answer directly — and in a patient well above ideal weight, the actual-weight version can be half as large again as the adjusted-weight version. FDA guidance is explicit that in overweight or obese individuals, using ideal or adjusted body weight "is likely to provide a more accurate estimate of renal function than using actual body weight". This calculator shows all three and, by default, follows the rule written into plazomicin labelling: use adjusted body weight when total weight exceeds ideal by 25% or more.
Where it breaks
A stable creatinine is assumed, so it does not apply in acute kidney injury, where creatinine lags the true clearance. Very low creatinine values — usually low muscle mass rather than good kidneys — inflate the result, because the equation divides by creatinine, and that is the direction that leads to overdosing. And the equation was fitted in the 1970s, before creatinine assays were standardised to the reference method modern laboratories are traceable to, so the creatinine values it was calibrated against are not quite the ones your laboratory reports.
Frequently asked questions
▸What is the Cockcroft-Gault formula?
Creatinine clearance in mL/min = (140 − age) × weight in kg ÷ (72 × serum creatinine in mg/dL), multiplied by 0.85 for women. It is written into FDA-approved labelling in exactly that form.
▸What is the difference between creatinine clearance and eGFR?
Creatinine clearance is in mL/min for the actual person; CKD-EPI eGFR is in mL/min per 1.73 m², normalised to a standard body size. Creatinine clearance also runs above true GFR because creatinine is secreted as well as filtered.
▸Which should I use for drug dosing?
Whichever the drug's own labelling specifies — usually Cockcroft-Gault, because the dose thresholds in that labelling were derived using it. FDA guidance adds that where an eGFR is used for dosing it should be converted to mL/min using the patient's own body surface area.
▸Should I use actual or ideal body weight?
FDA guidance says ideal or adjusted body weight is likely more accurate than actual weight in overweight or obese individuals. This calculator defaults to the plazomicin labelling rule: adjusted body weight once actual exceeds ideal by 25%.
▸Does it work in acute kidney injury?
No. Every steady-state equation assumes a stable creatinine. In acute injury the creatinine is still moving and lags the true clearance, so the estimate is wrong in a direction that depends on which way it is moving.
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