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Half-life calculator
Amount remaining, time elapsed or the half-life itself for decay and growth.
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About Half-life calculator
Radioactive decay and many other processes follow N = N0 x (1/2)^(t / half-life). Fill in any three of the four values to find the remaining amount, the elapsed time or the half-life. Switching to growth gives doubling time, useful for bacteria or investments.
How to use Half-life calculator
- Choose what you want to find: amount remaining, time elapsed or the half-life.
- Enter the known values, such as the starting amount and the half-life.
- Read the result for decay or growth below.
Why use this tool?
- Private: everything happens in your browser. Nothing you enter is uploaded.
- Free, with no sign-up, no watermark and no limit on how often you use it.
- Works on phones, tablets and computers: Android, iPhone, Windows, Mac and Linux. Nothing to install.
- Free to embed on your own website, with a ready-made code to copy.
- Available in 10 languages.
Also known as
Frequently asked questions
How much is left after three half-lives?
One eighth, or 12.5 percent. Each half-life cuts the remaining amount in half: 50 percent, then 25 percent, then 12.5 percent.
Does the time unit have to match the half-life unit?
Yes. If the half-life is in years, enter the elapsed time in years too. Mixing days and years is the most common reason for an answer that looks far too large or small.
Can I use this for growth and doubling time?
Yes. The same exponential math applies, so you can use it for things that double over a set period. Treat the real-world result as an estimate, because growth rarely stays perfectly steady.
Is Half-life calculator free?
Yes. Half-life calculator on Toolipedia is free to use, with no sign-up and no watermark.
Is it safe to use?
Yes. Everything is worked out in your browser, and nothing you enter is sent to our server.
Does it work on my phone?
Yes. It works in any modern browser on Android and iPhone, as well as on tablets and computers. There's nothing to install.
Do I need an account?
No. Just open the page and use the tool. There's no sign-up and no email needed.
Can I put Half-life calculator on my own website?
Yes. Use the Embed on your site button under the tool to copy a short piece of code and paste it into your page. It is free, needs no account, and the tool keeps working inside your page.