How to Find Z Score on TI-84

A z-score tells you how far a value is from the mean, measured in standard deviations. You can find a z-score on the TI-84 Plus CE in different ways, depending on the information given in the problem. Some questions provide the mean and standard deviation, while others give you a list of raw data and require the calculator to find them. This guide shows you how to find a z-score on the TI-84 Plus CE using both methods. It also explains how to find a p-value when the z-score is already known.

If you don’t have a physical device, you can also calculate on TI-84 online and follow the same steps in your browser.

The Z Score Formula

Before using the calculator, it’s good to understand its workings. The formula for a z score is:

z = (x − μ) / σ

In this formula, x is the value being tested, μ is the population mean, and σ is the standard deviation. A positive z score indicates the value is above the mean. A negative score means it is below the mean. A score near zero shows the value is close to average.

Method 1: Calculating a Z Score Manually

This method for finding a z score on TI-84 works best when the mean and standard deviation are already given in the problem, so the calculator only needs to handle the arithmetic.

Turn on the calculator and press the HOME key to reach the main screen.
Type the formula directly using the known values: (x − mean) / standard deviation.
Press ENTER to see the result.

For example, with a value of 82, a mean of 75, and a standard deviation of 4, typing (82 − 75) / 4 and pressing ENTER returns 1.75. That means the value 82 sits 1.75 standard deviations above the mean.

Method 2: Finding a Z Score From a List of Data

This method for finding a z score on the TI-84 is useful when analyzing a full dataset. It works well when the mean and standard deviation are not provided in advance.

Press STAT, choose EDIT, and enter each data value into list L1.
Press STAT again, arrow over to CALC, and select 1-Var Stats.
Confirm the list is set to L1 and press ENTER.
Note the mean, shown as x-bar, and the standard deviation, shown as Sx for a sample or σx for a full population.
Return to the home screen and calculate (value − mean) / standard deviation using the numbers just found.

Using the same formula with different values gives the z score for each entry in the dataset. You don’t need to retype the whole thing.

How to Find P Value From Z Score on TI-84

Once a z score is known, converting it into a p value uses a completely different function on the calculator.

Press 2ND, then VARS to open the DISTR menu.
Select normalcdf from the list.
Enter the values in this order: normalcdf(lower bound, upper bound, mean, standard deviation).

For a standard normal distribution, the mean is 0 and the standard deviation is 1. To find the probability below a z score of 1.5, type normalcdf(-99, 1.5, 0, 1) and press ENTER. The result, 0.9332, means about 93.3 percent of values fall below that point on the curve. Typing -99 and 99 in place of negative and positive infinity works fine for most classroom level problems.

Common Mistakes to Watch For

Small mistakes often appear in this type of calculation. Catching them early can prevent confusion on tests or homework.

Mixing up Sx and σx, since one applies to a sample and the other to a full population.
Dropping the negative sign when a value sits below the mean.
Rounding the standard deviation too early, which throws off the final result slightly.
Entering values in the wrong order inside normalcdf, since the format always follows lower bound, upper bound, mean, standard deviation.

Storing the mean and standard deviation as variables after running 1-Var Stats helps avoid retyping long decimals. Press STO and then a letter to save that value as A or B. You can reuse these in the z-score formula for every value in a dataset.

FAQs

Yes, as long as the mean and standard deviation are already known, finding a z score on TI-84 with the manual formula method works without needing a full dataset.

Sx represents the standard deviation of a sample, while σx represents the standard deviation of an entire population. Using the wrong one gives a slightly inaccurate z score.

The normalcdf function handles this conversion. Entering the z score as the upper bound along with a mean of 0 and standard deviation of 1 returns the probability tied to that score.

Yes, the button sequence and menus described above apply directly to the TI-84 Plus CE along with older TI-84 Plus models.

Conclusion

Finding a z score on the TI-84 depends on the method you choose. You can either plug numbers into a formula or use 1-Var Stats for a dataset. Once you know the basics, switching between z scores and p values is quick. For more on what the calculator can do beyond statistics, check the TI-84 usage tips page.