Exact model
A shared birthday in a room of 40
- Probability:
- 89.1%
- Odds:
- 8.2 to 1
- dBan
- +9.1 dBan
With 40 people in the room, about 89 in 100 modelled groups contain a shared birthday.
Calculation
p = 1 − ∏ₖ₌₀³⁹ (365 − k) / 365 ≈ 0.89123181
Assumptions
Birthdays are independent and equally spread over 365 dates. Leap days are ignored.
Sources
- Uniform 365-day birthday model