Radioactive Decay Calculator

How to use

After each half-life, half of the previous amount remains in the simple exponential-decay model, including fractional or multiple half-lives.

1. Enter N₀.
2. Enter half-life.
3. Enter elapsed time in the same unit.
4. Review remaining, decayed and percentage.

How it is calculated

Example

If N₀=100, half-life is 5 years and elapsed time is 10 years, 25 units remain: 25%.

Important notes

Assumes constant half-life and a closed sample; decay chains and daughter products are not modeled.

Frequently asked questions