Birthday Paradox Calculator
Simulate and calculate the famous birthday paradox. Gain visual and mathematical clarity into why a group of 23 people triggers a 50.7% shared odds.
Why is the mathematical rate so high?
While we intuitively compare our birthday against everyone else (which requires 253 people to cross 50%), the math of the paradox checks for ANY pair of people who share a birthday. With 23 people, there are 253 possible pairs. Each pair is a new chance for a cosmic coincidence.
Frequently Asked Questions
The birthday paradox is the counterintuitive probability finding that in a group of just 23 randomly chosen people, there is a greater than 50% chance that at least two of them share a birthday.
It is surprising because we confuse "someone sharing a birthday with ME" (which is rare) with "ANY TWO people sharing a birthday" (which has many more possible pairs).