Is caffeine gone after one half-life?

No. One half-life leaves about half of that dose. Each following half-life clears about half of what is still left.

Can a phone app measure my half-life?

No. A half-life setting is an assumption you choose. Measuring your own clearance takes clinical testing.

Do small sources belong on the chart?

They can. Gum, soda, supplements, and decaf still add milligrams, and those milligrams follow the same kind of curve.

What happens when you log another drink?

The model adds another dose at its logged time. Each dose then contributes its own declining estimate to the total.

Guide

How to Read a Caffeine Half-Life Chart

Read a caffeine half-life chart using a worked example. See why the curve falls gradually and how dose, time, and your chosen assumption change the estimate.

Updated October 21, 2026 2 min read

Caffeine Tracker is free to download.

Short answer

A caffeine half-life chart estimates how much of a logged dose remains over time. With an assumed five-hour half-life, 100 mg becomes 50 mg after five hours and 25 mg after ten. The curve is a model, and changing the half-life changes the result. It doesn't measure your body’s clearance.

A caffeine curve can look nearly flat late in the day without reaching zero. To read it, separate the calculation from the assumption behind it. The table below uses a five-hour half-life only to make the arithmetic easy to follow.

A 100 mg example

Time after entry	Estimated caffeine	Share remaining
Start	100 mg	100%
5 hours	50 mg	50%
10 hours	25 mg	25%
15 hours	12.5 mg	12.5%

This is a single-dose exponential-decay example with a five-hour assumption. The formula is dose × 0.5 raised to (hours elapsed ÷ half-life). Several drinks contribute separate declining amounts that are added together at the time you inspect.

What the half-life is counting

The interval halves what remains from a dose. It doesn’t subtract the same number of milligrams each time. In a five-hour example, the first interval removes 50 mg from 100 mg, while the next removes 25 mg from the remaining 50 mg.

Read the horizontal axis as time and the vertical axis as an estimated amount. A line reaching 50 mg after one half-life still represents caffeine in the model. It hasn’t reached zero.

Why your number can differ from the average

Treat the selected half-life as an assumption. The FDA notes that sensitivity and clearance differ between people. A phone diary cannot determine your biological value.

Changing the setting moves the whole estimated curve, even if every logged drink stays the same. Use that difference to understand the model’s uncertainty. Feeling alert or sleepy on one evening doesn’t validate a half-life setting.

How to read a remaining-caffeine chart

Log the sources you want the chart to include, with an amount and time for each. Coffee, tea, energy drinks, and supplements can all belong in the diary. Missing an entry makes the model incomplete.

Then read a specific time, such as your usual bedtime, instead of treating the whole curve as a score. The number at that time comes from the doses you logged and the half-life you selected. It can help you compare a 3 p.m. coffee with a 6 p.m. coffee.

Chart the half-life you selected

Caffeine Tracker draws an estimated curve from the drinks you log, the half-life you select, and your usual bedtime. You can inspect a point on the chart, including the time around a drink. The result is informational.