Birthday Paradox Calculator

The Birthday Paradox is a famous probability result: in a group of just 23 people, there is a greater than 50% probability that two people share a birthday. This surprises most people because 23 seems small compared to 365 days. The probability grows rapidly — with 70 people it exceeds 99.9%. It is called a paradox not because it is logically contradictory, but because it strongly violates intuition.