Half-Life Calculator — Free Online Tool

The half-life calculator uses the exponential decay equation to find the remaining amount, elapsed time or half-life of a radioactive sample. Just leave the value you want to compute empty.

How to Use

1. Enter the initial amount of the sample
2. Fill in two of half-life, remaining amount or elapsed time
3. Leave the value you want to compute empty
4. Click Calculate and read the result

Key Features

• Presets for Carbon-14, Radon-222 and more
• Solve for remaining, time or half-life
• Decay percentage shown instantly
• One-click copy

FAQ

What is a half-life?

Half-life is the time required for a radioactive sample to decay to half of its initial amount, such as the 5,730 years of Carbon-14.

How is the remaining amount calculated?

The tool uses A = A0 × (0.5)^(t / T). You can also solve for elapsed time or half-life by leaving that field empty.

Is this tool free?

Yes, it runs entirely in your browser and your inputs are never uploaded.

Can I use it for carbon dating?

Yes — select the Carbon-14 preset and leave the elapsed-time field empty to compute the age of a sample.