Birthday Paradox Calculator
Calculate the probability of shared birthdays in a group of people
About this calculator
The Birthday Paradox Calculator determines the probability that at least two people in a group share the same birthday. This surprising mathematical phenomenon shows that in a group of just 23 people, there's over a 50% chance of a shared birthday, defying most people's intuition. This calculator is valuable for understanding probability theory, planning events, analyzing coincidences, and educational purposes in mathematics and statistics courses.
How to use
Simply enter the number of people in your group into the calculator. The tool will instantly compute and display the probability percentage that at least two people share the same birthday. You can experiment with different group sizes to see how the probability changes dramatically as you add more people.
Frequently asked questions
Why is it called a paradox?
It's called a paradox because the results are counterintuitive - most people expect you'd need many more people for a 50% chance of shared birthdays.
What assumptions does this calculator make?
The calculator assumes 365 days per year, ignoring leap years, and that all birthdays are equally likely to occur on any day.
At what group size is there a 50% probability?
With just 23 people in a group, there's approximately a 50.73% chance that at least two people share the same birthday.