Your team is favored by 8 points. How likely does this make them to win?
In college basketball, there is a 77% chance a team favored by 8 points will win. In fact, each point in the spread increases the chance of winning by about 3.5%. A good rule of thumb is that 50%+(3.5 x spread) will get you within 1-2% of the chance of the favorite winning. However, this rule only applies up to about 11 point spreads at which point each additional point added to the spread is worth significantly less than 3.5% additional chance of winning.
Using 22,215 college basketball games played from November 2012 to January 2018, the actual data is displayed below in table format.
| Spread | Games | Percentage of Games Won by Favorite |
|---|---|---|
| 1 | 703 | 52.7% |
| 1.5 | 913 | 54.7% |
| 2 | 1,010 | 55.3% |
| 2.5 | 1,117 | 56.9% |
| 3 | 1,002 | 60.6% |
| 3.5 | 1,025 | 60.0% |
| 4 | 995 | 62.3% |
| 4.5 | 999 | 66.4% |
| 5 | 892 | 66.8% |
| 5.5 | 960 | 71.1% |
| 6 | 848 | 69.8% |
| 6.5 | 860 | 70.3% |
| 7 | 781 | 76.6% |
| 7.5 | 804 | 77.1% |
| 8 | 710 | 77.0% |
| 8.5 | 678 | 80.3% |
| 9 | 577 | 81.1% |
| 9.5 | 599 | 84.8% |
| 10 | 540 | 82.2% |
| 10.5 | 499 | 84.9% |
| 11 | 452 | 85.8% |
| 11.5 | 416 | 89.6% |
| 12 | 378 | 89.1% |
| 12.5 | 399 | 83.9% |
| 13 | 362 | 89.7% |
| 13.5 | 330 | 90% |
| 14 | 301 | 92.3% |
| 14.5 | 279 | 92.4% |
| 15 | 258 | 95.7% |
| 15.5 | 242 | 96.6% |
| 16 | 193 | 94.8% |
| 16.5 | 191 | 95.2% |
| 17 | 191 | 93.1% |
| 17.5 | 128 | 96.8% |
| 18 | 153 | 98.0% |
| 18.5 | 123 | 95.1% |
| 19 | 117 | 98.2% |
| 19.5 | 101 | 99.0% |
| 20 or more | 1,089 | 98.5% |
Here is the table data in chart form. As you can see, a relatively straight line until 20 points at which point the n-size per spread drops below 100 and the chance of winning stays relatively flat at 98%-99%.
View the table data in chart form.
Notes
- The highest spread with an underdog winner was 25.5. Interestingly, 3 teams won with that spread.
- Spreads above 20 are rare, accounting for less than 5% of all games with a spread.
Gamblers Analytics 