Compare calculators

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

Birthday Paradox Calculator

Calculate the probability that at least two people in a group share a birthday. Useful for teaching probability concepts or settling that classic party debate.

Group Size (Number of People)

Days in Year

Calculate Probability For

Result Format

Fill in the required fields to see your result.

Probability

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

Fill in the required fields to see your result.

Key differences

	Birthday Paradox Calculator	Chi-Square Test Calculator
Category	Probability	Probability
Inputs required	4	4
Result	Result	Chi-Square Statistic
What it does	Calculate the probability that at least two people in a group share a birthday. Useful for teaching probability concepts or settling that classic party debate.	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.