P-value Calculator — from z, t, or Chi-Square

Use this free p-value calculator to convert a z, t, or chi-square test statistic into a p-value. Choose one-tailed or two-tailed, and see whether the result is significant at the 0.05 level, with step-by-step working.

What the p-value means

The p-value is the probability of getting a test statistic at least as extreme as yours if the null hypothesis were true. A small p-value (typically below 0.05) is evidence against the null hypothesis.

How to use it

1. Pick the distribution (z, t, or χ²) and the tail.
2. Enter the statistic (and degrees of freedom for t and χ²).
3. Press Find p-value.

Related: the Z-Score Calculator and more free math calculators.

Frequently asked questions

What is the p-value in statistics?

The p-value is the probability of getting a test statistic at least as extreme as yours if the null hypothesis were true. A small p-value means your result would be unusual under the null hypothesis. For example, a two-tailed z of 1.96 gives p ≈ 0.05, and z = 2.58 gives p ≈ 0.01, so a larger statistic means a smaller p-value.

How do you find the p-value using a calculator?

Choose the distribution that matches your test (z, t or chi-square), pick one-tailed or two-tailed, and enter the test statistic plus degrees of freedom if needed. The calculator returns the p-value and flags whether it is below 0.05. For a z-test with z = 2.0, the two-tailed p-value is about 0.0455, and the one-tailed value is about 0.0228.

How do you find the p-value on a TI-84 calculator?

Press STAT, move to TESTS, and choose the test that fits your problem, such as Z-Test or T-Test. Enter your data or summary statistics, pick the alternative (≠, < or >), and select Calculate; the screen shows p. If you already have the test statistic, normalcdf (for z) or tcdf (for t) in the DISTR menu gives the tail area directly.

How do you find the p-value for a t-test?

Compute the t statistic, find the degrees of freedom (n − 1 for a one-sample test), and find the tail area of the t distribution beyond your statistic. Double it for a two-tailed test. For t = 2.1 with 15 degrees of freedom, the two-tailed p-value is about 0.053, just above the usual 0.05 cutoff.

How do you find the p-value without a calculator?

Use a printed z, t or chi-square table. Look up your test statistic, read the tail area, and double it for a two-tailed test. For z = 1.50, the standard normal table gives 0.9332 to the left, so the right tail is 0.0668 and the two-tailed p-value is about 0.134. For t and chi-square, tables list only a few cutoffs, so you get a range rather than an exact p.

Is a p-value a percentage?

A p-value is a probability between 0 and 1, so it is usually written as a decimal, like 0.03. You can describe it as 3%, meaning there is a 3% chance of a result at least this extreme if the null hypothesis is true. It is not the chance that the null hypothesis itself is true, which is a common misreading.

How to use the P-value Calculator for homework

The P-value Calculator is most useful when you treat it as a learning check, not just a shortcut to the final answer. Start by copying the original problem carefully, including signs, exponents, decimal points, fractions, parentheses, and units. Then enter the values in the same order the problem gives them. A small typing change can completely change the result, especially in algebra, statistics, geometry, and probability problems.

Before you press the button to calculate, make a quick estimate or prediction. The estimate does not need to be exact. Its job is to help you notice impossible answers. If a distance becomes negative, a probability is bigger than 1, an angle looks too large, or a decimal point seems misplaced, go back and check the input before trusting the final result.

Before you enter the problem

• Rewrite the problem in a clean line so every value is easy to see.
• Use parentheses around grouped expressions, especially in fractions and exponents.
• Keep units with the numbers while you work, even if the calculator only asks for the numbers.
• Check whether the problem wants an exact value, a decimal approximation, or a rounded answer.
• Look for restrictions such as positive values only, a chosen interval, or a required domain.

How to read the result

After the calculator gives a result, read more than the final line. If steps, tables, graphs, or intermediate values are shown, use them to understand how the answer was built. That is especially important when you are studying for a quiz or test, because teachers often give more credit for a correct process than for an unsupported number.

Try to identify the main idea behind the result. For example, ask yourself which formula was used, which operation changed the expression, which value controlled the graph, or which assumption made the answer possible. When you can explain that idea in your own words, the tool has helped you learn the skill instead of only checking one problem.

Common mistakes to avoid

Turn the answer into practice

One good way to study is to solve the problem by hand first, then use the P-value Calculator to check your work. If your answer is wrong, do not erase everything immediately. Find the first line where your work stops matching the calculator’s logic. That line is usually where the real misunderstanding happened.

1. Work the problem on paper and circle your final answer.
2. Use the calculator to check the result.
3. If the answers match, write one sentence explaining the method.
4. If they do not match, compare each step until you find the first difference.
5. Redo a similar problem without the tool to make sure the correction sticks.

When to use a calculator and when to work by hand

Use the P-value Calculator when you want to check a long calculation, explore a pattern, test a graph, or confirm a result after practicing. Work by hand when the assignment asks for steps, when you are learning a new method, or when the test will not allow a digital tool. The strongest students use both: hand work to build understanding and calculators to check accuracy.

If you are preparing for a timed test, practice some problems without the tool and some with it. That balance helps you build speed while still understanding the math. Over time, the goal is to need the calculator less often for routine steps and use it more strategically for checking, exploring, and confirming your reasoning.

Quick accuracy checklist

Before you leave the page, use the P-value Calculator result to answer three quick questions: What was the input? What rule, formula, or method connects the input to the result? What would change if one number in the problem changed? These questions turn a single calculator answer into a reusable math skill.

For homework, write the original problem, the calculator’s result, and one short explanation of the method in your notebook. For test review, cover the result and try to reproduce the setup on your own. If you can set up a similar problem without looking back at the calculator, you are much closer to owning the skill.