Et G Alcohol Detection Time Calculator

How the EtG Alcohol Detection Time Calculator Works

Ethylglucuronide (EtG) is a direct, phase-II metabolite of ethanol produced in the liver and excreted in urine. Unlike blood alcohol concentration (BAC), EtG persists in urine long after ethanol itself has been eliminated, making it the preferred biomarker for recent alcohol use in workplace testing, probation monitoring programs, and clinical alcohol treatment settings. This calculator uses a two-stage pharmacokinetic model to estimate how long EtG will remain above a given laboratory cutoff threshold.

Stage 1: Estimating Peak EtG Concentration

Peak urinary EtG concentration is estimated using a Widmark-style distribution model adapted for EtG pharmacokinetics:

C_peak = (D × 14) / (W_kg × r) × k

• D — Total standard drinks consumed. One standard drink contains exactly 14 grams of pure ethanol, equivalent to 12 oz of regular beer, 5 oz of table wine, or 1.5 oz of distilled spirits.
• W_kg — Body weight converted to kilograms by dividing pounds by 2.205.
• r — Widmark distribution factor: 0.68 for biological males and 0.55 for biological females, reflecting the higher proportion of lean body mass and total body water in males, which distributes ethanol across a larger volume and lowers peak EtG per drink.
• k — A urinary EtG scaling constant derived from published clinical excretion studies, converting the BAC-equivalent output to approximate ng/mL EtG units.

The sex-based difference in the r-factor is clinically significant: a 150 lb biological female consuming the same number of drinks as a 150 lb biological male will produce roughly 24% higher estimated peak EtG levels, extending the predicted detection window. This reflects pharmacokinetic data reviewed by Wurst et al. in their foundational study on ethylglucuronide as a marker of recent alcohol use.

Stage 2: First-Order Elimination Kinetics

EtG is eliminated from urine following first-order kinetics, meaning its concentration decreases by a constant percentage per unit time regardless of starting concentration. The urinary EtG concentration at any elapsed time after peak is expressed as:

C_current = C_peak × (0.5)^{(t_elapsed / t_½)}

Clinical research published in Helander & Beck (2014) via PMC and the SAMHSA Advisory on the Role of Biomarkers in Alcohol Use Disorder Treatment establishes the urinary EtG half-life (t_½) at approximately 2.5 to 3 hours under standard conditions. Hydration level, urine pH, kidney function, and individual metabolic rate can shift this range in either direction, contributing to inter-individual variability in real-world test results.

Stage 3: Calculating Remaining Detection Time

The core detection time estimate solves for how many additional hours remain before EtG concentration drops below the selected cutoff (C_cutoff):

t_remaining = log₂(C_current / C_cutoff) × t_½

This derivation follows directly from the exponential decay equation: solving for the time at which C_current × (0.5)^(t/t_½) equals C_cutoff yields the logarithmic expression above. A positive result indicates EtG is still above the cutoff; a zero or negative result means the person has already cleared that threshold.

Understanding Cutoff Thresholds

Cutoff selection dramatically affects the detection window and the meaning of a positive result:

• 100 ng/mL — The most sensitive threshold, recommended by SAMHSA for clinical treatment monitoring and abstinence verification. Can detect even light drinking (1–2 drinks) up to 24 hours later, and heavy consumption (6+ drinks) up to 72–80 hours later. Higher sensitivity increases the risk of false positives from incidental ethanol exposure.
• 500 ng/mL — The standard workplace and forensic cutoff. Reduces false positives from mouthwash, hand sanitizer, and fermented food sources while still detecting meaningful consumption within approximately 12–36 hours depending on intake level.

Worked Example

A 185 lb (84 kg) biological male consumes 5 standard drinks and finishes at 10 PM. At 9 AM the following morning (11 hours elapsed), using r = 0.68 and t_½ = 2.5 hours, the calculator computes C_peak, applies 11 hours of first-order decay to obtain C_current, and then calculates t_remaining at both cutoffs. At the 100 ng/mL threshold, he may remain detectable for several more hours; at 500 ng/mL, he would likely be below threshold. This distinction has direct consequences for individuals enrolled in EtG-based alcohol monitoring programs.

Important Limitations

This calculator produces a population-level statistical estimate, not a guaranteed individual result. Diuretic use, kidney disease, extreme hydration or dehydration, and specimen adulteration all affect real-world EtG concentrations in ways no formula can fully capture. No calculator can replace confirmatory GC-MS or LC-MS/MS laboratory analysis. Use this tool for educational planning only, and consult a qualified healthcare provider or forensic toxicologist for any legally or medically consequential decision.