What this calculator does
Creatinine is a waste product the kidneys clear at a fairly steady rate, so its level in the blood indicates how well they are filtering. The Cockcroft-Gault equation turns that into an estimated clearance in millilitres per minute.
Age matters as much as the creatinine value. The same 1.0 mg/dL creatinine in a 75 kg man gives an estimated 115 mL/min at 30 years old and 63 mL/min at 80, which is why age-adjusted dosing exists.
The formula
Subtract age from 140, multiply by weight in kilograms, apply a factor of 0.85 for women, and divide by 72 times the serum creatinine.
| Term | Meaning |
|---|---|
| Creatinine clearance | An estimate of how much blood the kidneys clear of creatinine per minute. |
| Cockcroft-Gault | The 1976 equation used here, still standard for many drug dosing decisions. |
| eGFR | A different estimate from equations such as CKD-EPI, which laboratories usually report instead. |
The inputs explained
| Field | What to enter |
|---|---|
| Age (years) | Age in years. |
| Weight (kg) | Body weight in kilograms. Which weight to use, actual or ideal, depends on the clinical context. |
| Serum creatinine (mg/dL) | Serum creatinine in mg/dL. |
| Sex | Sex, which applies a 0.85 factor for women reflecting average differences in muscle mass. |
When to use it
Checking a drug dose
Many medicines are renally cleared and are dosed against Cockcroft-Gault specifically.
Understanding a kidney function result
Seeing how age and weight enter the estimate explains why creatinine alone is not enough.
Following a trend
A series of estimates over time is more informative than any single value.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How much does age change the estimate?
The same creatinine at four ages.
| Age | Estimated creatinine clearance | Note |
|---|---|---|
| 30 years | 115 mL/min | An estimate of kidney function, not a substitute for a lab-measured GFR. |
| 50 years | 94 mL/min | An estimate of kidney function, not a substitute for a lab-measured GFR. |
| 70 years | 73 mL/min | An estimate of kidney function, not a substitute for a lab-measured GFR. |
| 80 years | 63 mL/min | An estimate of kidney function, not a substitute for a lab-measured GFR. |
Questions
How does this differ from eGFR?
They are different equations estimating related but not identical things. Laboratories usually report eGFR from CKD-EPI, while Cockcroft-Gault remains the reference for many drug dosing guidelines. The two do not always agree and are not interchangeable.
Which weight should be used?
It depends on the purpose and on body composition. Actual, ideal and adjusted body weight are all used in different dosing protocols, and the choice can change the answer substantially in obesity. A pharmacist or clinician should confirm which applies.
Why is there a factor for women?
Because creatinine comes from muscle, and the equation uses an average correction for differences in muscle mass. Like all population averages it fits some individuals poorly, particularly those with unusually high or low muscle mass.
When is the estimate unreliable?
In rapidly changing kidney function, extremes of body size or muscle mass, pregnancy, and after a high-protein meal or creatine supplementation. It assumes a steady state that is not always present.
For another panel value needing adjustment, see the corrected calcium calculator. For the unmeasured ion balance, see the anion gap calculator.