Online Tools and Calculators > Math > Half Life Calculator

Half Life Calculator

Fill in any three to calculate the fourth value.
Quantity remains N(t):
Initial quantity N0:
Time t:
Half-life t1/2:
Plese enter 3 and only 3 numbers. Leave ONE field blank.

About Half Life Calculator

The online 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.

Half-life Calculation Formula in Exponential Decay

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

Exponential Decay Formula

N(t) = the quantity that still remains and has not yet decayed after a time t
N0 = the initial quantity of the substance that will decay
t1/2 = the half-life of the decaying quantity


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