Birthday Paradox Calculator
Result
Birthday Paradox Calculator Find the surprising probability that two people in a group share a birthday. Enter the number of people and this calculator returns the chance of at least one shared birthday, the chance of none, the group size needed to cross — free online calculator.
Formula
- Birthday Paradox Calculator calculates its result from Number of people. It uses the formula P(at least one shared birthday) = 1 − product of distinct-birthday probabilities.. Change any input to recalculate the result instantly.
- The main inputs are Number of people. Enter them in the units and format shown in the calculator.
- Keep comparable quantities in compatible units whenever the formula combines or compares them.
- Changing any input above recalculates the result with the same calculation engine used by this page.
Example: Birthday Paradox
- Number of people: 23
Using Number of people = 23, the calculated result is 50.7297234324.
Sample result: Calculating…
Frequently asked questions
What does the Birthday Paradox calculate?
Birthday Paradox Calculator Find the surprising probability that two people in a group share a birthday. Enter the number of people and this calculator returns the chance of at least one shared birthday, the chance of none, the group size needed to cross — free online calculator.
Which values should I enter?
Enter Number of people using the units and format shown beside each field.
What formula does this calculator use?
The calculator uses the following relationship: P(at least one shared birthday) = 1 − product of distinct-birthday probabilities..
Why might my result differ from another source?
Results can differ when another source uses different units, rounding rules, conventions or assumptions. Compare the inputs and definitions before comparing results.
Does the result update automatically?
Yes. Changing an input updates the result using the same calculation engine shown on this page.