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The Half-Life Calculator is used to calculate the half-life in exponential decay.

*Half-life* is the period of time it takes for a substance undergoing decay to decrease by half. It is usually used to describe quantities undergoing exponential decay (for example, radioactive decay) where the half-life is constant over the whole life of the decay, and is a characteristic unit (a natural unit of scale) for the exponential decay equation. However, a half-life can also be defined for non-exponential decay processes, although in these cases the half-life varies throughout the decay process.

The calculation of half-life used in this tool is based on the exponential decay equation.

An exponential decay process can be described by the following formula:

where:

N(t) = the quantity that still remains and has not yet decayed after a time t

N_{0} = the initial quantity of the substance that will decay

t_{1/2} = the half-life of the decaying quantity