How long it lasts, and how much is left at bedtime.

A cappuccino at four in the afternoon

Call it 130 mg, which is roughly what a double-shot drink carries. At a five hour half-life, 7 hours later at 23:00 there is still about 49 mg of it in you. That is not far off a fresh single espresso, at the hour you were planning to sleep.

Work it out for your own coffee →

This is the part a daily total cannot tell you. Two people can drink the same 400 mg and go to bed in completely different states, because what matters is not how much went in but when.

What common drinks carry

Reference values by drink and brew method, not a measurement of your particular cup. Beans, dose, grind and extraction all move the real number, sometimes a long way.

The published reference points

These are population figures from EFSA and the FDA for healthy adults. They are not targets, and they are not advice for you specifically.

Where the five hours is wrong

A single half-life is a simplification, and it is worth knowing how it fails. Between healthy adults the real figure ranges roughly three to seven hours, and genetics account for most of that spread. It runs considerably longer in pregnancy and for people on oral contraceptives, and shorter for smokers. Absorption is not instant either: blood levels peak thirty to sixty minutes after drinking, so the first half hour is overstated by any model that assumes it all arrives at once.

So treat every figure here as an estimate of an estimate. It is enough to see the shape of a day, which is the useful part, and not enough to be a measurement of you.

Your own curve, without the arithmetic

My Coffee Shelf estimates the caffeine in every brew you log, follows it through the day, and shows how much is still with you at bedtime. Swipe back through the week to see the pattern. On iPhone it writes each brew to Apple Health, so the total counts tea and everything else too.