Creatinine clearance calculator: Cockcroft-Gault next to eGFR
Creatinine clearance and eGFR both estimate how well your kidneys filter, from the same creatinine result. eGFR is what your lab prints. Creatinine clearance, by the 1976 Cockcroft-Gault equation, is still what many drug labels use for dose adjustments, so pharmacists and prescribers often calculate it alongside. The two can differ by 20 or 30%, especially in older, smaller, or heavier people. Enter your creatinine, age, and weight to see both. Height is optional and adds the ideal and adjusted weight versions.
The Cockcroft-Gault equation
Cockcroft and Gault fitted it to 24-hour urine collections from 249 men:
Creatinine clearance (mL/min) = (140 − age) × weight in kg ÷ (72 × creatinine in mg/dL)
For women, multiply by 0.85. That factor was an estimate in the original paper, not measured. A creatinine in µmol/L is divided by 88.4 first.
The result is in mL/min for your actual body, not scaled to an average size. That’s the main reason it differs from eGFR, which is in mL/min per 1.73m² of body surface.
Which weight to use
The equation was built on actual weight, in people who mostly weren’t obese. Creatinine comes from muscle, and in someone well above their ideal weight, much of the extra weight isn’t muscle, so actual weight overestimates clearance. With a height, the calculator also shows:
- Ideal weight by the Devine formula: 50 kg for men and 45.5 kg for women, plus 2.3 kg for each inch over 5 feet. It’s shown only when you weigh more than it.
- Adjusted weight: ideal weight plus 40% of the difference between actual and ideal. It’s shown when you weigh more than 120% of ideal, which is when many pharmacy protocols switch to it.
Which one a prescriber uses depends on the drug and local practice. The calculator shows all of them rather than picking.
Creatinine clearance and eGFR compared
| Age | Sex | Weight | Height | Cockcroft-Gault | eGFR 2021 | eGFR for size |
|---|---|---|---|---|---|---|
| 65 | Female | 70 kg | 165 cm | 62 | 63 | 65 |
| 80 | Female | 55 kg | 160 cm | 35 | 51 | 46 |
| 45 | Male | 120 kg | 178 cm | 158 (121 adjusted) | 95 | 133 |
| 30 | Male | 90 kg | 183 cm | 115 | 83 | 103 |
Creatinine 1.0 mg/dL, except 1.1 in the second row and 1.2 in the fourth. Cockcroft-Gault and eGFR for size in mL/min; eGFR 2021 in mL/min/1.73m².
Two things drive the gap. Age counts more in Cockcroft-Gault: the (140 − age) term falls faster than eGFR’s age term, so for older adults clearance usually reads lower. In the second row, an 80-year-old with an eGFR of 51 has a clearance of 35, which would change the dose of several drugs. Size counts only in Cockcroft-Gault, since eGFR is scaled to an average body. “eGFR for size” removes that scaling by multiplying by your body surface area (by the Mosteller formula) and dividing by 1.73, so it can be compared with clearance directly.
Why both are still in use
The KDIGO guideline uses eGFR for diagnosing and staging kidney disease, and most labs now report the race-free CKD-EPI 2021 equation. Many drug labels, though, were written from studies that measured kidney function with Cockcroft-Gault, and their dose tables still use it. Neither number is “right”. They answer different questions. The eGFR calculator covers eGFR and the CKD stages.
Limits
- Creatinine has to be stable. Both equations assume your creatinine is steady. After sudden kidney injury, creatinine lags behind the real change, and neither estimate is reliable.
- Muscle mass. Very muscular people, amputees, and people with severe muscle loss make unusual amounts of creatinine, so both estimates are off. A cystatin C result or a measured 24-hour clearance can settle it.
- Creatinine assay. Cockcroft-Gault predates today’s standardized creatinine tests, which read slightly lower than the old ones. That pushes Cockcroft-Gault results up a little compared with the original study.
Tracking kidney function over time
How to track your eGFR over time covers what counts as a real change, how much creatinine varies between draws, and what can push it up for reasons that have nothing to do with your kidneys.
Creatinine clearance in HealthViewer
HealthViewer is a lab results tracker that runs on your own computer. It imports creatinine and eGFR from lab report PDFs, MyChart downloads, and direct connections to your health system, and charts each over time in Trends. The overlay view puts them on one chart, so a step in eGFR with flat creatinine shows up as an equation change rather than a decline.
Everything stays in an encrypted file on your computer, with no account and no cloud service. Getting Started walks through the first import.
This calculator is for understanding your results, not for choosing a drug dose. Drug dosing depends on more than kidney function. Leave it to your prescriber and pharmacist.