# Half-life Calculator - Exponential decay

Below we have a half-life calculator. A half-life is the period of time it takes for a substance undergoing decay to decrease by half.

The formulas below are used in calculations involving the exponential decay of, for example, radioactive materials...

### Examples - Calculate half-life

Let’s suppose that a well-known substance decomposes in water into chloride and sodium ions according to the law of exponential decay. If the initial amount of the substance is 24 kg and after 10 hours, 14 kg are left, how much substance is left after 1 day? How long does it take until 0.25 kg is left?

First, we solve for the half-life; second, we solve for the ending amount; finally, we solve for the time considered in the formulas.

We can use the calculator like this...

Exponential Decay / Half-Life

Beginning amount = 24 kg
Final amount = 14 kg
Elapsed time = 10 h

Half-Life = 12.86 h

Beginning amount = 24 kg
Half-life = 12.86 h
Elapsed time =  24 h

Final amount =  6.5828 kg

Beginning amount = 24 kg
Final amount =  0.25 kg
Half-life = 12.86 h

Elapsed time = 84.6826 h