Disclaimer: This calculator is offered freely as a helpful tool. All outputs should be independently verified, and the user is solely responsible for the use of the calculator and any results. Radformation disclaims any warranties and is not responsible for how this tool is utilized or the results it provides.

Radioactive Decay Calculator

Here, we present a radioactive decay calculator, which calculates the amount of radioactive activity a substance will have after decaying for a given time. The formula for radioactive decay is derived from the familiar exponential decay formula and is as follows:

This formula determines the amount of activity (A) present after some elapsed time (t) as a function of the initial activity (A₀) and the substance's half-life (T_1/2).

How To Use The Calculator

Selecting an isotope from the drop-down will automatically populate the half-life field (the provided half-life can be edited as desired). If the isotope you're looking for is not included in our shortlist, select 'Custom' in the drop-down menu and use a half-life corresponding to the isotope you'd like to calculate.

Units for each entry are typed directly into the calculator text fields as shown by the example text. Initial activity units can be any unit. Supported time units include:

• ns/nanoseconds
• us/microseconds
• ms/milliseconds
• s/seconds
• m/mins/minutes
• h/hrs/hours
• d/days
• y/years
• centuries
• millennia