Nuclear Decay Half-Life Calculator – Radioactive Decay

Enter the half-life

Input the half-life of the radioactive substance in your chosen time unit.

Input initial amount and elapsed time

Enter the starting quantity and how much time has passed since then.

Calculate remaining amount

Click Remaining to see how much of the substance is left after the elapsed time.

Use consistent time units

Ensure half-life and elapsed time use the same unit (both seconds, both years, etc.).

Remember the 10 half-life rule

After 10 half-lives, less than 0.1% of the original material remains — effectively gone.

Decay is random but predictable

Individual atom decay is random, but large samples follow the half-life pattern precisely.

Half-life cannot be changed

Temperature, pressure, and chemical state do not affect radioactive decay rates.