EtG Half-Life Calculator
Model how an estimated EtG level falls over time using exponential decay.
Note: US workplace cutoffs are typically 500 ng/mL or 100 ng/mL. Detection windows vary from 24 to 80 hours.
Ethyl glucuronide (EtG) is a byproduct the body forms after drinking alcohol, and it's the marker some alcohol tests look for. This calculator illustrates how a given EtG concentration would fall over time under a simple exponential-decay model, given a starting level and a half-life. It's a teaching tool for understanding half-life maths — it cannot tell you what a real test will show. Everything is calculated in your browser.
The decay formula
The calculator applies standard exponential decay, halving the concentration once per half-life:
Current = Initial × (½)^(hours ÷ half-life)
With a starting level of 1,000 ng/mL and a 3-hour half-life, after 9 hours you've passed three half-lives, leaving about 125 ng/mL. It also shows how many half-lives have elapsed and compares the result to common reference cutoffs such as 100 and 500 ng/mL. Change the half-life field to see how sensitive the outcome is to that single assumption — small changes compound quickly over many hours.
Why this can't predict a real test result
Real EtG behaviour is far messier than one clean curve. The starting concentration, the true half-life, hydration, kidney function, the amount and timing of drinking, and the specific test all vary enormously from person to person and even day to day, so published detection windows range widely — often quoted anywhere from about a day to several days. This model assumes a single fixed half-life and a known starting point, neither of which you can actually measure at home. Treat it purely as an illustration of decay maths, not as a way to anticipate or influence a test, and follow the guidance of the program or professional administering any real testing.
Frequently Asked Questions
Can this tell me whether I'll pass an EtG test?
No. It is a simplified model that assumes a fixed half-life and a starting level you can't truly measure. Real EtG clearance varies widely between people and situations, so the tool cannot predict an actual test outcome.
What half-life should I enter?
EtG half-life estimates vary, and the tool defaults to a commonly cited figure of around 3 hours. Because the result is highly sensitive to this number, treat any single value as an assumption rather than a fact.
What do the cutoff labels mean?
Some laboratories use reference thresholds such as 100 or 500 ng/mL when interpreting results. The labels here simply show where the modelled value falls relative to those common figures; actual cutoffs depend on the specific test and program.
Is my data saved?
No. The calculation runs entirely in your browser and nothing you enter is uploaded or stored.