Half-Life Calculator
Fill in the values and the answer updates as you type.
How the Half-Life Calculator works
Remaining = initial × (½)^(time ÷ half-life). Use the same time unit for both values.
Inputs and results
The Half-Life Calculator takes 3 inputs and gives 3 results.
What you enter
- Initial amount — starts at 100.
- Half-life — starts at 5730.
- Elapsed time (same unit as half-life) — starts at 10000.
What you get
- Amount remaining
- Percent remaining
- Percent decayed
Example: Half-Life Calculator with the starting values
With initial amount 100, half-life 5730 and elapsed time (same unit as half-life) 10000, the calculator returns:
| Amount remaining | 29.8292 |
|---|---|
| Percent remaining | 29.83% |
| Percent decayed | 70.17% |
Change any value above and the results update straight away.
Half-Life Calculator FAQ
How do I use the Half-Life Calculator?
Enter initial amount, half-life and elapsed time (same unit as half-life) in the fields, then read amount remaining, percent remaining and percent decayed in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Half-Life Calculator calculate?
Amount of a substance left after a given time. It returns amount remaining, percent remaining and percent decayed from the 3 values you provide.
What values does the Half-Life Calculator start with?
It opens with initial amount 100, half-life 5730 and elapsed time (same unit as half-life) 10000 so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Half-Life Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Half-Life Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.