How to Find a Z-Score on a TI-84

A z-score answers one question: how many standard deviations is a value away from the mean? It turns any raw value into a number on a common scale, which is what makes it possible to compare a test score, a height, and a stock return using the exact same yardstick.

The formula

z = (x - μ) / σ

x is the value you’re checking, μ is the mean, and σ is the standard deviation. A z-score of 2 means the value sits two standard deviations above the mean; -1.5 means one and a half standard deviations below it.

Where the numbers come from

There’s no single dedicated “z-score” button on a TI-84 — you get μ and σ from 1-Var Stats on your data set, then compute z as a plain arithmetic expression using those two numbers. It’s a two-step process: run the stats, then do the subtraction and division by hand (or let the calculator do it for you as one expression).

Worked example

For a data set with μ = 68 and σ = 4, a value of x = 74 gives z = (74 - 68) / 4 = 1.5 — a point and a half above average.

Try it yourself

On the TI-84 Calculator, run 1-Var Stats in Tools → Lists & Stats to get x̄ and Sx for your data, then type the z-score formula directly into the calculator’s expression line using those two numbers, e.g. (74-68)/4. If you need the probability associated with a z-score rather than the score itself, that’s what Tools → Distributions → normalcdf and invNorm are for.