Caffeine Half-Life Calculator
Track how much caffeine remains in your system over time, using your own half-life.
Five hours is the average, and the spread is enormous
Caffeine's half-life in healthy adults averages about five hours, but ranges from under two to more than nine depending on genetics, liver enzymes, smoking and oral contraceptives. Pregnancy can extend it beyond fifteen. If a 3 pm coffee keeps you awake and your colleague's does not, that difference is real and mostly inherited.
The formula
Remaining = dose × (½)^(hours / half-life)
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Caffeine Half-Life Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
Caffeine Half-Life Calculator — frequently asked questions
Is this caffeine half-life calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the caffeine half-life calculator.
- caffeine half-life calculator
- caffeine metabolism
- coffee before bed calculator
- caffeine in my system
- how long does caffeine last
- caffeine half life calculator
About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed August 23, 2026 · Calculation runs client-side · No data collected · Report an error