How long does caffeine stay in your system?

The half-life, and why it is a range

Caffeine is cleared mostly by one liver enzyme, and the speed of that enzyme varies a lot between people. The commonly cited half-life — the time for half a dose to leave — is about five hours in a healthy adult. The US Institute of Medicine’s review put the range at roughly 1.5 to 9.5 hours; the FDA states four to six. Smoking speeds clearance up; pregnancy, oral contraceptives and some medicines slow it down, sometimes dramatically.

So the curve on this page, drawn for a typical five-hour half-life with the FDA’s four-to-six-hour band shaded, is a model of an average adult. If you know you are sensitive, read it as a floor.

Working the numbers

Start with the dose. Brewed coffee is about 96 mg per 8-ounce cup; espresso about 64 mg per shot; black tea 47 mg; green tea 28 mg; a can of cola 33 mg; an energy shot 200 mg. The caffeine-by-drink pages list twelve drinks with their reported ranges.

Then halve it every five hours. A 96 mg coffee at 3 pm is about 48 mg at 8 pm, 24 mg at 1 am and 12 mg at 6 am. An espresso at 5 pm is 32 mg at 10 pm. A 200 mg energy shot at noon is still 50 mg at 10 pm and 25 mg at 3 am.

The last-coffee calculator does this for any drink, time and bedtime.

The six-hour trial

Most advice about caffeine timing is extrapolated from the half-life. One study measured sleep directly. In 2013 Drake and colleagues gave healthy adults 400 mg of caffeine — about four cups of coffee — at bedtime, three hours before, or six hours before, on different nights, with a placebo night for comparison, and recorded sleep in a laboratory. Even the six-hour dose reduced total sleep by more than an hour. The part that matters most: on the six-hour night, participants’ own diaries showed no difference. They thought they had slept normally.

That is the basis for the six-hour cutoff on the caffeine cutoff pages. The trial used a large dose; a single cup is likely to cost less. But the direction is clear, and the fact that people cannot feel the loss is a good reason not to trust “coffee never affects my sleep”.

What counts as “gone”

On the curve, caffeine never reaches zero; it just keeps halving. For planning, this site uses 25 mg — a quarter of a cup of coffee, about what a cup of decaf might contain at the high end — as the line under which timing stops mattering much. It is an illustrative threshold, chosen by us, not a clinical one. A 96 mg coffee takes about ten hours to cross it at the average half-life; a 200 mg energy shot takes fifteen.

Daily total

The FDA considers up to 400 mg a day generally safe for healthy adults — roughly four 8-ounce cups of brewed coffee. That figure is about overall health, not sleep; for sleep, the timing of the last 100 mg matters more than the day’s total.

Questions people ask

How long until caffeine is completely gone?

It never hits zero on the curve, but after five half-lives — about 25 hours — less than 3% remains. In practice, under 25 mg (about a quarter cup) is a useful planning line.

Why does coffee not affect my sleep?

It may be affecting it without you noticing: in the 2013 trial, people given caffeine six hours before bed slept an hour less by the lab's measure but reported no difference. Or you may be a fast metaboliser; smokers, for example, clear caffeine faster.

Does decaf have caffeine?

A little: typically 2 to 15 mg a cup, against about 96 for regular brewed coffee.