Statistics & probability
Shared birthday probability
Explore the chance of a matching category in a group.
A clear answer. Here’s how.
Probability of at least one match = 1−product(1−i/categories) for i=0…people−1, calculated with logarithms. Returns 1 when draws exceed categories. Assumes independent equally likely categories; real birthdays are seasonal and leap days are not represented by the default model.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Number of independent draws / people
- 23
- Equally likely categories / possible birthdays
- 365
Example result
- At least one matching pair
- 0.507297234324
- No matching pair
- 0.492702765676