# Half-life

## Calculate initial quantity, half-life, elapsed time and final quantity

## How to use the half-life calculator

This calculator lets you calculate the following:

- What quantity is left, given an initial quantity, the half-life and the elapsed time.
- How long it takes to reach a certain value, given an initial quantity and the half-life.
- What half-life is needed to reach a certain quantity in a certain time, given an initial quantity.
- What initial amount is needed ti reach a certain quantity after a certain time, give the half-life.

Select the variable you'd like to calculate

The half-life is the time it takes for a quantity to decrease to half of its original size. The term is frequently used when making calculations related to radioactive decay.

Read more about half-life here: http://en.wikipedia.org/wiki/Half-life