The birthday paradox
How many people before a shared birthday becomes likely?
THE EXPERIMENTReady when you are
No steps yet. The observed result will appear here.
Your saved comparisons
Kept for this page session. Reloading clears them.
Share your setup
Try it together.
Share the page, or choose to include your setup. Entered names are always omitted from team-picker links.
How it works
How it works.
Compare observed shared birthdays with 1 − ∏(365 − k)/365.
Assumptions and limits
365 equally likely birthdays, independent people; leap days and seasonal patterns excluded.