Compare calculators

Both calculators run independently — change the inputs on either side to compare results.

Chi-Square Test Calculator

Calculate the chi-square (χ²) test statistic and compare it against a critical value to test goodness of fit or independence. Used in research, biology, marketing, and quality control.

Observed Frequency 1

Expected Frequency 1

Observed Frequency 2

Expected Frequency 2

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Probability

Birthday Paradox Calculator

Find the surprisingly high probability that at least two people in a group share a birthday. Use it to demonstrate why coincidences are far more likely than intuition suggests.

Number of People (people)

Days in Year (days)

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Key differences

	Chi-Square Test Calculator	Birthday Paradox Calculator
Category	Probability	Probability
Inputs required	4	2
Result	Chi-Square Statistic	Probability of Match
What it does	Calculate the chi-square (χ²) test statistic and compare it against a critical value to test goodness of fit or independence. Used in research, biology, marketing, and quality control.	Find the surprisingly high probability that at least two people in a group share a birthday. Use it to demonstrate why coincidences are far more likely than intuition suggests.