The formula
How to calculate creatinine clearance
The Cockcroft-Gault equation estimates creatinine clearance as a proxy for kidney function. It dates from 1976 and remains in use because most drug dosing guidance was validated against it.
The constants shown apply when creatinine is measured in µmol/L, as UK laboratories report it. In units of mg/dL the formula divides by 72 instead, with the same 0.85 adjustment for women.
The calculator asks for:
- Age (years)
- Weight (kg)
- Serum creatinine (µmol/L)
No submit button: type and the answer moves. Your inputs end up in the link, so the page can be shared already filled in.
If an exact figure for one of the fields is not available, a careful estimate is a reasonable starting point, since the calculator recomputes instantly the moment a more accurate number is available — nothing here depends on getting every field exact on the first pass.
Why creatinine clearance matters
This kind of calculation gets used both out of general interest and ahead of a specific conversation — with a trainer, a midwife or a GP — where having an actual number ready, rather than a description, makes that conversation more concrete and specific.
This tends to get checked before or after a change in routine — a new training block, a change in diet, a different stage of a pregnancy — as a way of putting a figure on something that would otherwise only be felt rather than measured.
A single number like this is most useful placed in context rather than read in isolation. Reference ranges exist because bodies vary considerably and still count as healthy across a wide spread of values, so a result sitting outside a commonly quoted range is a prompt to look more closely rather than a verdict on its own. The same figure, tracked consistently over time, tends to say more than any single reading ever will.
Where a result depends on more than one measurement, small errors in each input tend to compound rather than cancel out — a slightly mismeasured waist and a slightly mismeasured height, taken together, can shift a derived figure more than either error would on its own. Taking each measurement carefully, and ideally twice, is worth the extra minute it takes.
Worked example
Take the figures the calculator starts with:
- Age: 62 years
- Weight: 78 kg
- Serum creatinine: 95 µmol/L
That gives:
- Creatinine clearance, male: 78.77 ml/min
- Creatinine clearance, female: 66.6 ml/min
- Creatinine in mg/dL: 1.07
Those starting figures exist only to show the calculation working, not as a target or a reference value to compare yourself against — replace them with your own measurements in the calculator above and the same formula applies exactly as shown.
Reading the result
Above 90 ml/min is generally normal, 60–89 mildly reduced, 30–59 moderately reduced and below 30 severely reduced. Which weight to use — actual, ideal or adjusted — depends on the drug and the guideline.
Where this goes wrong. The equation performs poorly at extremes of body weight, in acute kidney injury where creatinine has not yet equilibrated, and in people with very low muscle mass. Dosing decisions belong with a clinician and the relevant protocol.
As with any general-purpose formula, the result here is an estimate derived from population averages, not a measurement specific to you — a reasonable starting point for a conversation with a qualified professional, not a replacement for one. Nothing on this page is medical advice.
eGFR from the CKD-EPI equation is preferred for staging chronic kidney disease. Cockcroft-Gault is still specified for many drug dose adjustments, because that is what the licensing studies used.
Because creatinine is produced by muscle, and muscle mass scales with body weight. Two people with identical serum creatinine but very different builds have different clearances.
The headline figure is creatinine clearance, male. With 62 years age, 78 kg weight and 95 µmol/L serum creatinine, that comes to 78.77 ml/min. Change any field and the figure moves with it.
It uses a published formula applied exactly as defined, so the arithmetic itself is precise — but the formula is a population-level estimate, and individual results can vary from it for reasons the formula has no way to account for. Treat the output as a reasonable estimate rather than a measured or diagnostic value.
For most people, yes — a single reading is a snapshot, while the same measurement repeated consistently over weeks or months shows a trend, which is generally more informative than any one figure taken in isolation.
Small differences between calculators usually come down to which published formula or reference dataset each one uses — several equations in this area exist in more than one accepted version. This page states the specific formula used in the section above, so it is possible to check directly whether another source is using the same one.