Caffeine day curve: what is still in you at bedtime

Enter what you drank and when. The chart draws how much caffeine is still in your body through the day, using first-order elimination at a half-life you set. It is a picture of a curve, not health advice, and the half-life it uses is the one number that varies most from person to person.

What the curve is doing

Caffeine leaves the body by first-order elimination, which means a constant fraction goes per unit of time rather than a constant amount. One half-life removes half of what is there, two removes three quarters, and so on. The chart adds up every drink you entered on that basis, so a second cup lands on top of whatever is left of the first.

The green line uses the half-life you picked. The shaded band behind it is the same drinks at a 3 hour half-life and at a 7 hour half-life, which is the range reported for adults in a 2017 review of caffeine safety in Frontiers in Psychiatry. The 5 hour default is the figure StatPearls gives for the average adult.

Half-life varies per person, and it varies a lot

This is the part that makes the chart yours rather than everyone's. StatPearls puts the average adult at about 5 hours, then lists the things that move it: smoking cuts it by up to half, late pregnancy can stretch it to around 15 hours, liver disease and drugs that inhibit the same liver enzymes stretch it, and newborns are in a different world entirely. The FDA makes the same point in plainer words, that there is wide variation in both how sensitive people are to caffeine and how fast they clear it.

So the band on the chart is not decoration. If you have never measured which end of it you are on, treat the whole band as your answer rather than the line.

Where the model is optimistic

Two simplifications worth knowing about. First, each drink is treated as landing in your bloodstream the moment you drink it, whereas serum caffeine actually peaks around two hours after a drink, so the first hour or two of each step is drawn higher and earlier than it really is. Second, a single half-life is applied all day, which ignores that your own clearance shifts with what else you have eaten, taken, or done.

The drink figures come from the Barista Life caffeine feed, where every entry carries the source it was checked against.

The 400 mg number, in context

The FDA cites 400 mg a day for most healthy adults as an amount not generally associated with negative effects, and notes that too much varies from person to person with body weight, medications, medical conditions, and individual sensitivity. That is a figure about daily intake. It is not a ceiling on the curve above, and this page is not the place to work out what your number should be. If caffeine and sleep is the actual question, that is one for a doctor, not a chart.

FAQ

What half-life should I use? Adults are commonly reported in a 3 to 7 hour range, with about 5 hours as the average. The tool defaults to 5 and lets you move it because there is no single right answer across people.

Why is there still caffeine in the chart the next morning? First-order elimination never reaches zero, it just halves repeatedly. After five half-lives roughly 3 percent of a dose is left, which for a large afternoon drink is still a measurable amount.

Where do the caffeine figures come from? The drink list is generated from the Barista Life caffeine feed, where each entry carries a source URL and the date it was last checked.

Does this tell me when to stop drinking coffee? No. It draws the curve for the drinks you enter. What to do about that curve is between you and, if it matters, your doctor.