Shared birthday experiment
Explore why shared birthdays become likely in a moderately sized group. The model deliberately treats all 365 dates as equally likely.
Your inputs
Start with the example values, then replace them with your own. For tables, keep the vertical bar separators and use a dot for decimals.
This is an educational model with simplified assumptions and a pseudorandom generator. Do not use its results as a forecast or for gambling decisions.
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Result and workspace
Use the start button to open your result or activity.
How it works
P(match) = 1 − Π(1 − k / 365), k = 0…n−1. Birthdays are independent and uniformly distributed; leap days are excluded.
Worked example
These sample results use the original example inputs in the form. They do not change when you edit your inputs; your own result appears in the workspace.
- Theoretical match probability: 50.7297 %
- Simulated match frequency: 51.1 %
Read the result carefully
Results depend on the values and assumptions shown above. Change one input at a time to see its effect. A blank or unavailable result means the data does not support a calculation; it is not zero.