Exact model
A shared birthday in a room of 30
- Probability:
- 70.6%
- Odds:
- 2.4 to 1
- dBan
- +3.8 dBan
In a room of 30 people, a shared birthday is already more likely than not: it appears in about 71 in 100 modelled groups.
Calculation
p = 1 − ∏ₖ₌₀²⁹ (365 − k) / 365 ≈ 0.70631624
Assumptions
Birthdays are independent and equally spread over 365 dates. Leap days are ignored.
Sources
- Uniform 365-day birthday model