Half-life

Number of half-lives elapsed	Fraction remaining	Percentage remaining
0	1/1	100
1	1/2	50
2	1/4	25
3	1/8	12	.5
4	1/16	6	.25
5	1/32	3	.125
6	1/64	1	.563
7	1/128	0	.781
...	...	...
$n$	$1/2^n$	$100(1/2^n)$

A radioactive half-life is the amount of time that it takes for a mass of a given element to decay to one half of its original mass.

The table at the right shows the amount of element left after each half-life. At the bottom is the most general form of the half-life equation.