How long does caffeine last? A practical timeline

Using EFSA's population-average half-life, about half the starting dose remains. A 120 mg coffee becomes an estimated 60 mg; a 200 mg energy drink becomes about 100 mg. These are illustrations, not blood measurements.

Someone who clears caffeine quickly may be below that estimate. Someone with slower clearance may be well above it. The range becomes especially important when the drink was large or bedtime is close.

Two four-hour half-lives leave about one quarter of the original dose. That is roughly 30 mg from 120 mg or 50 mg from 200 mg. A slower half-life leaves more.

This long tail explains why a mid-afternoon drink can overlap with bedtime even when the noticeable stimulation disappeared before dinner.

Sleep can be affected without a dramatic buzz, and people who use caffeine regularly may feel less of a given dose. Neither observation proves the caffeine has cleared.

Judge the practical duration by outcomes: how readily you fall asleep, whether sleep is broken, and how you feel the next day. Those outcomes matter more than whether you can still feel the coffee.

Doses overlap. If an estimated 50 mg remains when you drink another 100 mg, the model now starts the next interval near 150 mg. Small drinks can therefore produce a sizeable late-day total.

A useful log records time and milligrams for every source. “Three coffees” is much harder to interpret because serving sizes and brewing methods vary.

A calculator is for ordinary planning. Very large doses, especially concentrated caffeine powders or supplements, can be dangerous.

If the amount was large or unknown, or symptoms are severe, seek urgent help from local medical or poison-control services. For ongoing sleep trouble, discuss the full pattern with a clinician because caffeine may be only one part of it.

Suppose a person drinks 140 mg at 8 a.m. and another 80 mg at 2 p.m. With a four-hour half-life, the first dose has fallen to about 18 mg by 8 p.m.; the second is near 28 mg. Together, the rough estimate is about 46 mg even though neither drink felt especially large.

Change the half-life to eight hours and the same schedule looks very different: about 50 mg from the morning dose and about 48 mg from the afternoon dose remain, for a total near 97 mg. The example is not a personal prediction. It shows why recording dose, time, and overlapping drinks matters more than asking when the last cup “wore off.”