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Caffeine Half-Life Calculator

How much caffeine might be left after 6 hours?

Enter the caffeine you had, the hours since and a half-life to see how much a model says is left.

One Click Answers · Caffeine Half-Life Calculator
oneclickanswers.com/caffeine-half-life-calculator · Printed
About this tool & how to use it

What it does

Models how much of an amount of caffeine is left after some hours for a half-life you choose. It is a model, not a measurement of you.

How to use it

  1. Enter the milligrams of caffeine and the hours since you had it.
  2. Enter the half-life in hours that you want to use. 5 hours is a common starting value.
  3. Read the amount left and the share of the original.

This is YOUR assumption: 5 is only a starting value. People differ a lot, and the pages read for this tool gave no single figure to rely on, so change it to explore.

One click answer

Your answer will appear here.

Fill in the form and your answer appears here as you type.

Assumptions

  • The half-life is the number you enter. It is not a measurement of you.
  • Smoking, some medicines, pregnancy and liver conditions change how fast caffeine clears.
  • The page does not say when it is safe to sleep or drive.

Printed from oneclickanswers.com. Results are estimates based on what was entered; see the assumptions above.

How it works

Left = amount x 0.5 ^ (hours / half-life). 200 mg after 6 hours at a 5-hour half-life is 200 x 0.5^1.2, about 87 mg.

The pharmacology review that was read (Frontiers in Pharmacology, 2021) says half-life varies widely between people and gave no single figure, so the page does not claim one and you choose it.

MedlinePlus says effects may continue for four to six hours.

Formulas and details
  • Left = amount x 0.5 ^ (hours / half-life).

Assumptions

  • The half-life is the number you enter. It is not a measurement of you.
  • Smoking, some medicines, pregnancy and liver conditions change how fast caffeine clears.
  • The page does not say when it is safe to sleep or drive.

Example

Input: The starting values already in the form

Result: With a 5-hour half-life, about 87 mg of the 200 mg would be left after 6 hours. That is about 44% of what you had. It is a model, not a measurement of you.

Questions

What half-life should I use?

The sources do not give one figure for everyone, so there is no single right number. Try several to see how the result moves.

Will I sleep if the amount left is small?

The page does not say. It models an amount of caffeine, not your sleep.

Last reviewed 2026-10-04.

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