Caffeine Calculator

In short Two questions come out of a day of coffee: how much caffeine was that, and how much of it is still in me now. The first has no exact answer and the second does. CAFFEINE CONTENT IS A RANGE, NOT A NUMBER. A 240 ml filter coffee is anywhere from 80 to 120 mg depending on bean, roast, grind, dose and brew method, and robusta carries roughly twice the caffeine of arabica before anyone touches the recipe. Anyone quoting a single figure to the milligram is inventing precision. This page shows a typical value and the plausible range beside it, and the range is the honest answer. THE DECAY IS EXACT. Caffeine leaves the body with a half-life of about five hours, so half is gone after five, a quarter after ten and an eighth after fifteen. That is why the timing matters more than the total: a coffee at two in the afternoon still has a quarter of its caffeine in you at midnight, and for many people that is the difference between sleeping and not. Several drinks simply add up, each decaying from its own time, which is what this page computes. Your own half-life is probably not five hours. The real range across healthy adults is roughly three to seven, and it moves a long way with circumstance — smoking roughly halves it, while pregnancy can stretch it to fifteen hours or more, and oral contraceptives and several common medicines lengthen it substantially. If caffeine keeps you awake far longer than this page suggests, the likeliest explanation is simply that your half-life is longer than five hours; change the figure and the page will follow. On the guidance figures: EFSA and the FDA both use 400 mg a day as the amount not expected to cause concern for most healthy adults, and 200 mg in pregnancy. Those are population guidance rather than thresholds — nobody becomes unwell at 401 mg, and a great many people are uncomfortable well below 400. This page is arithmetic, not medical advice.