How to Convert a Money Line into a Percentage and Vice-Versa

This summer I read a book that is essential reading for any sports bettor, beginner, or expert.  The book is called Weighing the Odds in Sports Betting by King Yao.  In this book Yao explains how to think about and beat sports betting.  He draws from his successful career in financial derivative markets and examines sports betting in that vein.  Chapters on general sports betting include information on the sports-betting market, different ways to beat sports betting, scalping, middling, hedging, tips for bettors and handicappers, how to evaluate other handicappers and an enlightening interview with a Las Vegas professional bettor.

In Chapter 1, Yao shows the reader How to convert a money line into a percentage.

Convert a money line into its equivalent win percentage by dividing the amount you risk by the amount your ticket will be worth if your bet wins.  The ticket amount is your win plus the amount you bet.

If the money line is negative, then take the money line and divide it by itself minus 100.  For example, a money line of -129 converts to 56.3%:

=-129 / (-129 -100)

=-129 / -229

=56.3%

If the money line is positive, then take 100 and divide ti by the money line plus 100.  For example, a money line of +109 is converted to 47.8%

=100 / (109+100)

=100 / 209

=47.8%

Converting percentage into a money line

If the percentage is greater than 50%, then divide it by 100% minus itself, and multiply by -100.  For example, 55% is conveted to -122

= PERC / (100% – PERC) x (-100)

= 55% / (100% – 55%) x (-100)

= 55% / 45% x -100

= 1.22 x -100

= -122

If the percentage is less than 50%, then take 100% minus itself divided by itself, then multiply by +100, then put a plus sign in front of it.  For example, 45% is converted to +122

= (100% – PERC) / PERC x 100

= (100% – 45%) / 45% x 100

= 55% / 45% x 100

= 1.22 x 100

= +122

So how is this useful?

I use the later set of formula’s (Converting percentages into money lines) every time I place a bet.  Sometimes I can cap my own games and determine that Team A has a 66% chance to win a game.  Other times, I use ESPNinsider to simulate the games for me (this requires a premium subscription).  In my sports betting Excel spreadsheet, I already have the two formula’s entered in so all I have to do is substitute the percentages to get my money line.

So let’s say that ESPN says Alabama has a 66% chance to beat Tennessee.  Using the formula above, I determine that based on that percentage, the money line should be Alabama -194.  At this point, the Alabama money line is actually only -170, so basically ESPN’s simulation says there is a -24 point value in taking Alabama.  You see what I’m saying? This is also helpful with line movement in that it quantifies in cents how much value that bet has gained or lost since it opened.