Explore the surprising probability of shared birthdays
With 23 people, there are 253 pairwise comparisons (23 × 22 / 2).
Each pair has a 1/365 ≈ 0.27% chance of matching birthdays.
Combined, these give approximately 50.7% probability of at least one match!
People often think: "What's the chance someone shares MY birthday?" (much lower)
The actual question: "What's the chance ANY two people share a birthday?" (much higher)
| Group Size | Probability of Match | Number of Pairs |
|---|---|---|
| 10 | 11.7% | 45 |
| 20 | 41.1% | 190 |
| 23 | 50.7% | 253 |
| 30 | 70.6% | 435 |
| 50 | 97.0% | 1,225 |
| 70 | 99.9% | 2,415 |