# How do you find the z score of a percentile?

##### 1 Answer

Jan 31, 2018

Z = (x - mean)/standard deviation.

Assuming that the underlying distribution is normal, we can construct a formula to calculate z-score from given percentile T%.

Then

Note that InvNorm(T) is a TI function, similarly we can use excel function Norm.Inv(T, 0, 1)

For example, z-score of 30th percentile is InvNorm(0.3) = -0.52