Exact model
A shared birthday in a room of 20
- Probability:
- 41.1%
- Odds:
- 1 to 1.4
- dBan
- −1.6 dBan
Bring 20 people together and about 41 in 100 modelled groups contain a shared birthday.
Calculation
p = 1 − ∏ₖ₌₀¹⁹ (365 − k) / 365 ≈ 0.41143838
Assumptions
Birthdays are independent and equally spread over 365 dates. Leap days are ignored.
Sources
- Uniform 365-day birthday model