Creatinine clearance calculator
Work through the Cockcroft-Gault equation the way it was originally meant to be used — as a quick bedside calculation, not a black box. Fill in the four fields below and watch the marker move along the scale.
What This Worksheet Is Actually Calculating
Creatinine is a byproduct your muscles generate around the clock, and your kidneys pull it out of your bloodstream at a fairly predictable pace — assuming they're working normally. Measure how much creatinine shows up in a blood draw, plug in a few details about the person it came from, and you get a working estimate of how fast their kidneys are filtering overall. That estimate is what this worksheet produces.
It matters most in one specific, practical scenario: figuring out whether a standard medication dose is safe for someone whose kidneys are filtering more slowly than average. A slower filtration rate means drugs that exit the body through the kidneys can build up over time, and dosing has to account for that directly.
The Equation Itself
Cockcroft and Gault published this formula in 1976, built from data on hospitalized patients, specifically so it could be calculated at the bedside without waiting on a 24-hour urine collection. Decades later, it's still the reference formula named in most drug labeling for renal dose adjustments.
The 0.85 multiplier isn't a statement about kidney function differing by sex — it's a rough correction for average differences in muscle mass, since creatinine production scales with muscle, not with kidney health directly.
Three Different "Weights," and Why It Matters Which One You Use
This is the part of the calculation most worksheets skip past, and it's genuinely consequential for anyone outside an average body size.
| Weight Type | What It Represents | When It's Used |
|---|---|---|
| Actual body weight | What the scale says today. | Default input, appropriate for most people near their ideal weight. |
| Ideal body weight (IBW) | An estimate based on height alone, using the Devine formula. | Used as the basis for calculating adjusted weight; rarely plugged into the CrCl formula directly. |
| Adjusted body weight (ABW) | A blend: IBW plus 40% of the difference between actual and ideal weight. | Recommended once actual weight passes roughly 130% of IBW, since fat tissue doesn't produce creatinine the way muscle does. |
Using actual weight for someone well above their ideal weight tends to overstate their true clearance, because the formula assumes all of that extra mass is metabolically active tissue producing creatinine — which, for adipose tissue, it largely isn't. This worksheet checks for that automatically and surfaces the adjusted-weight option when it applies.
Reading Where the Marker Lands
The scale above splits into four rough zones, borrowed from standard kidney-function staging conventions:
| Zone | Range | General Meaning |
|---|---|---|
| Red | Below 30 | Significantly reduced. Typically prompts urgent evaluation and a full medication review. |
| Amber | 30–59 | Moderately reduced. Common threshold for adjusting doses of renally-cleared drugs. |
| Olive | 60–89 | Mildly reduced. Often unremarkable, especially with age, but worth monitoring. |
| Teal | 90 and above | Within the typical range for healthy filtration. |
Questions People Ask About This Calculation
Height feeds a separate, background calculation — estimating your ideal body weight — purely to check whether your actual weight is high enough that adjusted weight should be offered as an option. It never enters the core Cockcroft-Gault equation directly.
They're related but calculated differently. eGFR, typically via the CKD-EPI equation, normalizes for body surface area and skips weight entirely, while Cockcroft-Gault CrCl is weight-dependent. Drug dosing guidance frequently still references CrCl specifically because that's what was used in the original trials for many medications.
No — this is a reference calculation, not a dosing tool. Actual dose adjustments depend on the specific drug involved, your full lab picture, and clinical judgment from a prescriber or pharmacist. Treat this worksheet as a way to understand a number, not to act on it alone.
Yes, meaningfully. Because the formula assumes a typical relationship between body weight and muscle-driven creatinine production, it can be less accurate for people with unusually high or low muscle mass relative to their weight — including some athletes, amputees, or individuals with significant muscle wasting.
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16(1):31-41.
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650-655.
- Winter MA, et al. Impact of various weights and creatinine values on Cockcroft-Gault accuracy. Pharmacotherapy. 2012;32(7):604-612.
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease.