The Cockcroft-Gault equation estimates creatinine clearance from your age, weight, sex, and serum creatinine. Despite newer equations existing, pharmacists still reach for it because most drug dosing studies were built on its numbers.
Your visual report appears here
Fill in the form and press Calculate. You will get your number, an interpretation chip, and a personalized chart pack drawn instantly in your browser.
- Risk spectrum with your position marked
- Reference ranges from the original publication
- Shareable link, nothing stored
Scientific references
The equation that refuses to retire
Published in 1976, Cockcroft-Gault predates the personal computer, yet it survives for a practical reason. When pharmaceutical companies established dosing rules for kidney function over the past five decades, they used this equation. The FDA still accepts it on drug labels, so switching to a fancier estimate can actually misalign your number from the evidence behind your medication. That inertia keeps a 1976 formula on every hospital computer in the world.
How it builds the estimate
The formula starts with 140 minus age, a blunt acknowledgment that kidney function fades with time. It multiplies by body weight because creatinine comes from muscle and more muscle means more creatinine to clear. Dividing by serum creatinine times 72 converts the whole expression into milliliters per minute, and women receive a 15 percent reduction reflecting lower average muscle mass. The output estimates creatinine clearance rather than true GFR, and the two differ slightly because the kidney secretes a little creatinine beyond what it filters.
Why weight choice sparks debate
The equation assumes weight tracks muscle. In obesity it does not, since fat tissue produces almost no creatinine. Plug actual weight into the formula for someone with a BMI over 30 and the estimate overshoots, sometimes badly. Many pharmacists substitute ideal or adjusted body weight in that situation, and some hospitals automate the switch. The original paper studied mostly lean men, a limitation worth remembering whenever the result will drive a real dosing decision.
Reading the output
Healthy young adults typically clear 90 to 130 mL per minute. Values sliding under 60 suggest moderate impairment, under 30 severe. These thresholds appear verbatim in drug monographs, which is where the estimate earns its keep. If your result seems inconsistent with how you feel or with other labs, ask for a measured collection or a cystatin C based estimate as a cross check. Single numbers from any equation deserve confirmation before they change treatment.