How late can you drink coffee?

Caffeine half-life ranges roughly 3 to 7 hours across the population. If you metabolise slowly (high sensitivity), the same dose lingers longer, so the cutoff has to move earlier to compensate. Normal sensitivity assumes a 5-hour half-life — the median.

Mostly yes. Decaf coffee has 2 to 15mg per cup, well under the 25mg threshold the calculator uses. Decaf tea ranges higher (10 to 30mg), and decaf espresso varies wildly between brands. If you are sensitive, treat decaf as 30mg until you know your brand.

Tolerance lowers caffeine's perceived effect on alertness, but it does not change the half-life much. Regular drinkers may metabolise slightly faster, but the residual mg at bedtime is roughly the same as a non-tolerant drinker. The sleep disruption is similar even if the alertness boost feels weaker.

If a single afternoon coffee keeps you awake at 11 pm, you are high-sensitivity. Other markers: caffeine causes jitters in others around you but you are wired hours later, or you have CYP1A2 slow-metaboliser genotype on a 23andMe result. When in doubt, start with high.

Caffeine from any source metabolises through the same pathway, so the half-life math is identical. The differences between coffee, energy drinks, and tea are in absorption rate (how fast caffeine reaches peak blood level) and in supplementary ingredients. The cutoff math at 6+ hours out is dominated by half-life, not absorption.

The 5-hour normal half-life is the most commonly cited figure across pharmacology references (e.g., Drake et al. 2013, Journal of Clinical Sleep Medicine). The 3 and 7-hour bands for low and high sensitivity are based on the standard ±2 standard-deviation range across the studied population.