Statistics

Birthday Paradox Calculator

Find the chance two people share a birthday.

Calculated Output

Shared-birthday probability (%) 50.73

Formula: P = 1 − ∏(365−i)/365

Step-by-Step Breakdown

1. Values used:

2. Number of people = 23

4. Shared-birthday probability = 50.73%

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The math behind it

P(shared) = 1 − probability all are different = 1 − ∏(365−i)/365.

23 people → 50.7% chance of a match.

Why so few?

It counts every pair, not just matches to one person — pairs grow fast.