Creatinine Clearance Calculator (Cockcroft-Gault)

Creatinine is a waste product of muscle that the kidneys filter out. Creatinine clearance is the volume of blood cleared of it per minute, and it approximates the glomerular filtration rate — it runs a little higher, because the tubules also secrete some creatinine.

Two differences matter in practice. Cockcroft-Gault includes body weight, so a larger person gets a higher clearance for the same creatinine. And the result is in mL/min for that person, not mL/min/1.73 m² as eGFR is reported. The two numbers are therefore not interchangeable, and they can place the same patient in different dosing bands.

Cockcroft and Gault derived their equation with actual body weight. In people with obesity, actual weight overstates muscle mass — the source of creatinine — and the equation overestimates clearance. The FDA's 2024 guidance notes that ideal or adjusted body weight is likely to give a more accurate estimate in overweight or obese individuals.

This calculator shows all three and picks a headline by a common convention:

• Actual weight below ideal weight: use actual weight.
• Actual weight from 100% to 120% of ideal: use ideal weight.
• Actual weight above 120% of ideal: use adjusted weight (ideal + 0.4 × the excess).

That convention is widely taught but it is not universal. Some institutions use a different cut-off, some use adjusted weight for everyone above ideal, and some drug labels name a specific weight. Where the label or local protocol says which weight to use, follow it — that is why all three results are shown.

The FDA's March 2024 guidance on pharmacokinetic studies in renal impairment classifies renal function into four groups by estimated GFR or Cockcroft-Gault creatinine clearance, both in mL/min.

Two caveats. The guidance states that this classification is for designing dedicated renal impairment studies and is not intended for classifying kidney disease. And the dosing thresholds in an individual drug label do not always match these classes, so the label's own cut-offs take priority.

For decades, the pharmacokinetic studies that set renal dosing used Cockcroft-Gault to group participants, so the dose tables in older labels are written in its terms. The NIDDK notes that some older labels predate standardised calibration of creatinine assays, and that dosing for some older drugs may rest on equations that are no longer the most accurate.

Creatinine assays have since been standardised to isotope dilution mass spectrometry (IDMS). Modern standardised results tend to read lower than the assays of the 1970s, so the same patient can produce a higher Cockcroft-Gault clearance today than the equation's authors would have calculated. Current FDA guidance prefers eGFR for new pharmacokinetic studies but accepts either.

Some clinicians round a low serum creatinine up to 1.0 mg/dL (about 88 µmol/L) in older, frail or low-muscle-mass patients, on the reasoning that a very low creatinine reflects low muscle mass rather than excellent kidney function and would inflate the clearance. The practice is debated: it can also underestimate clearance and lead to underdosing.

This calculator does not round. It uses the creatinine you enter. If your protocol rounds, enter the rounded value yourself.

• Unstable kidney function, including acute kidney injury — creatinine lags behind changes in filtration, so the estimate trails reality.
• Extremes of muscle mass: very muscular people, amputees, people with paralysis, and frail or malnourished patients.
• Pregnancy, where filtration and body composition change substantially.
• Very high or very low body weight, where the choice of weight dominates the result.
• Drugs that block tubular creatinine secretion, such as trimethoprim, which raise creatinine without changing filtration.