eGFR / Creatinine Clearance Calculator

The eGFR result comes from the 2021 CKD-EPI creatinine equation, which combines your serum creatinine, age, and sex with a small set of published constants that change depending on whether your creatinine falls above or below a sex-specific threshold. It doesn't use race, height, or weight; eGFR is expressed per a standardized 1.73 m² body surface area, so two people of very different sizes can share the same eGFR.

The creatinine clearance result comes from the Cockcroft-Gault equation instead, which does factor in body weight alongside age, sex, and serum creatinine. Unlike eGFR, Cockcroft-Gault isn't normalized to a standard body size, so its result is a true mL/min flow rate rather than a rate calculated "per standard body size", one reason the two numbers can differ even when calculated from the same blood test.

Why the 2021 Equation, Not an Older One

Earlier CKD-EPI and MDRD equations included a coefficient that raised the estimated GFR for patients identified as Black. In 2021 the National Kidney Foundation and American Society of Nephrology jointly recommended removing it, concluding that race is a social construct rather than a biological variable that belongs in a kidney-function formula, and that the old adjustment could understate kidney disease in Black patients. This calculator uses only the race-free 2021 version.

A Note on Creatinine Clearance for Medication Dosing

The Cockcroft-Gault equation dates to 1976 and was validated on a study group of 249 white men, with its correction for women estimated rather than separately measured. Creatinine lab testing has also changed since then: assays were standardized industry-wide starting around 2011, which lowered typical reported creatinine values by roughly 12%, so a Cockcroft-Gault result calculated from a modern lab value tends to run higher than the equation's original 1976 validation assumed. For these reasons, the National Kidney Foundation now recommends moving toward BSA-adjusted eGFR for medication dosing decisions instead, and the FDA's 2024 industry guidance echoes the same shift for drug studies.

When you use the eGFR mode, your result is automatically matched to a CKD (chronic kidney disease) stage, the same G1 through G5 system nephrologists use to describe how much kidney function remains:

A single low reading isn't a diagnosis on its own. CKD is only confirmed when reduced eGFR, or another marker of kidney damage such as protein in the urine, persists for three months or longer. G1 and G2 specifically don't count as CKD unless other damage markers are present.

Age matters when reading your own stage. Kidney function naturally declines with age even without disease, by roughly 1 mL/min/1.73m² per year on average after about age 40, according to longitudinal aging studies. A G2 result in an otherwise healthy 75-year-old carries a different meaning than the same number in a 30-year-old, which is one reason a single reading is interpreted alongside your age and trend over time, not in isolation.

The two terms get used interchangeably in casual conversation, but they measure slightly different things. eGFR estimates glomerular filtration rate directly and is standardized to a reference body size, making it the basis for diagnosing and staging chronic kidney disease. Creatinine clearance measures how much creatinine your kidneys clear per minute, a close proxy for GFR that historically became the default for adjusting medication doses because the drug studies establishing safe dosing ranges were built using it.

In practice, for someone of roughly average body size, the two numbers usually land close together. They diverge more for people at the extremes of body weight, which is exactly why this calculator's creatinine clearance mode adjusts for ideal or obesity-adjusted body weight rather than always using your raw entered weight.

The Cockcroft-Gault formula was validated using ideal body weight, not actual weight, and using raw weight for someone significantly underweight or overweight can distort the result. This calculator follows the standard clinical correction: your ideal body weight is calculated from your height using the Devine formula, then compared to your actual weight through your BMI.

• BMI under 18.5 (underweight): your actual entered weight is used
• BMI 18.5 to 25 (normal range): your ideal body weight is used
• BMI 25 or higher (overweight or obese): an adjusted body weight, ideal weight plus 40% of the difference to your actual weight, is used

The result panel always shows which weight value was actually used in the calculation, along with your BMI, so the number displayed for your renally-cleared medication dosing is never a mystery.

Kidney function is often reviewed alongside a few other clinical numbers:

• Mean Arterial Pressure (MAP) Calculator: blood pressure and kidney function are closely linked and often reviewed together.