January 31, 2014
Gambling-math

Betting on the Super Bowl: Money Line vs. Win Percentage

As the Super Bowl approaches, I find myself in an interesting position where I want both teams to win. I grew up in Fort Collins, Colo., but have been living in Seattle for the past nine years. I spent the season rooting for both the Broncos and the Seahawks to do well, but now that they are playing each other, I’m conflicted.

So I’ve turned to gambling.

Football and Betting

The most common way to bet on football is against the spread, but I’m interested in the money line and how that can be used to calculate the gambling win percentage.

The Money Line

As I’m writing, the money lines for the big game from some websites are given in the chart below.

Team

Money Line #1

Money Line #2

Money Line #3

Denver

-135

-125

-140

Seattle

+115

+115

+120

A money line of -135 means you would have to bet $135 to win $100. Another way to think of it would be if you bet $135 you would take home $235 ($100 plus the $135 you originally bet). A money line of +115 means you bet $100 to win $115. Another way to think of it would be if you bet $100 you would take home $215 ($115 plus the $100 you originally bet).

Win Percentage

The money line feels backwards to the math teacher in me. A negative money line is favored to win against the positive money line. We can calculate win percentage using the money line to get a better idea of who is favored and by how much.

To calculate win percentage you take what you bet divided by what you take home if you win, and then turn that decimal into a percentage. Using the money line of -135 you would bet $135 to take home $235. So the win percentage associated with a money line of -135 is 135/235 or 57.5% (rounded to the nearest tenth of a percent).

Here is the same chart as above but as win percentage instead of the money line.

Team

Win % #1

Win % #2

Win % #3

Denver

57.4%

55.6%

58.3%

Seattle

46.5%

46.5%

45.5%

Sum of Win %

103.9%

102.1%

103.8%

Why the Bookies Win

When you add the win percentage of each team you get more than 100%. The extra percentage goes to the company where the bet is placed.

For example, if we look at Money Line No. 2, we see that the house will keep 2.1% of all the money bet with it, but will have to give some of that away once a champion has been crowned. If equal money was bet on both sides, then the house will get to keep half of the earnings, or 1.05% (half of 2.1%) of all the money bet with it.

Betting houses try to get equal money bet on each team, so you will see the money line change. The chart below shows the money line and win percentage from earlier in the week.

Team

Money Line

Win %

Denver

-115

54.5%

Seattle

-105

51.2%

Sum of Win %

105.7%

My Pick

Now that I know I can’t really win with gambling, I guess I’m cheering for a good close game. Ahh, who am I kidding…I’m rooting for the Broncos!

About the author:

Eddie Feeley is a middle school math teacher in Seattle, WA. In his free time he plays ultimate frisbee with the Seattle Rainmakers of Major League Ultimate.

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