Birthday Paradox Calculator
How likely is a shared birthday in a group?
Chance of any shared birthday
50.73%
Reference points
- 10 people: 11.7%
- 23 people: 50.7%
- 30 people: 70.6%
- 50 people: 97.0%
- 70 people: 99.9%
- 100 people: 99.99997%
About
Enter a group size and see the probability that at least two people share a birthday. The math surprises most people: in a room of 23, it's already over 50%. In 70, it's 99.9%.
How to use
- Enter the number of people.
- See the probability of any shared birthday.
FAQ
Why is the answer so high?+
Because you're not asking 'does someone share my birthday?' You're asking 'does any pair share?' With n people there are n × (n-1) / 2 pairs, which grows quadratically. Surprises happen at small n.