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

Statistical Power Calculator

Calculates the statistical power of a hypothesis test or the sample size needed to detect a given effect. Use it when designing experiments to ensure your study can reliably detect meaningful differences.

Effect Size (Cohen's d)

Significance Level (α)

Sample Size (per group) (participants)

Calculate

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Key differences

	Birthday Paradox Calculator	Statistical Power Calculator
Category	Probability	Probability
Inputs required	4	4
Result	Result	Statistical Power
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.	Calculates the statistical power of a hypothesis test or the sample size needed to detect a given effect. Use it when designing experiments to ensure your study can reliably detect meaningful differences.