Half-Life Decay Calculator
Calculate how much of a radioactive sample remains after a given time.
What this page needs from you
This page asks for initial amount, half-life in years and time elapsed in years. From those it returns remaining amount, together with fraction remaining, half-lives elapsed, decay constant and mean lifetime. Every figure updates as you type, and nothing you enter leaves your browser.
Where lab results and calculated results part company
These relations describe ideal behaviour: ideal gases, complete reactions, fully dissociated strong acids, no side products. Real yields fall short, real gases deviate near condensation, and real solutions show activity effects at higher concentrations. The calculated figure is the target to compare a measurement against, not a prediction of what the flask will contain.
The formula
N(t) = N₀ · (½)^(t / t½)
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 Half-Life Decay 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.
Half-Life Decay Calculator — frequently asked questions
Is this half-life decay 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
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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 September 14, 2026 · Calculation runs client-side · No data collected · Report an error