Half-life describes the time required for an amount of a substance to fall by half under a particular model. CoffeeBox applies the concept to caffeine and bedtime. The key point is persistence: feeling less stimulated does not prove that all caffeine has disappeared, and one average number cannot describe every person's elimination rate.
For a purely illustrative example, if a model assumes a five-hour half-life, an initial amount would fall to half after five hours and a quarter after ten. That arithmetic is not a measurement of your blood level or a prediction of your sleep. Repeated servings add another complication, as does uncertainty about how much caffeine each drink contained.
A controlled sleep study found disruption after a substantial fixed caffeine dose even six hours before bedtime. It does not establish one compulsory cutoff for every serving or individual. Use the concept to recognize why timing matters, then consider your own sleep pattern and all caffeine sources. If sleep problems persist, an equation or a supposed fast-metabolizer label should not replace an appropriate assessment of other possible causes.
The conversation
A good question can make a better brew.