Question of the Day - 20 June 2024

[Editor's Note: This answer was provided by Logan Fields, author of our book 20/20 Sports Betting.]

I agree, it seems a little intimidating, but it's not at all complicated to convert percentages into sports betting lines.  

Take the chance of winning (60%) and divide it by the chance of losing (40%). In this example, it's 1.5, which translates to a –150 line. Since you have a better-than-even chance of winning, the number will be negative and you’ll have to wager $150 to win $100. That's on the favorite. 

If you want to wager on the underdog with its 40% chance of winning, you make the same calculation, but express the bet as a positive +150, as you should be rewarded for winning a bet that has only a 40% chance. So a $100 wager would win $150 (plus the return of the original $100 you wagered).

Here are a couple more examples. An event that has a 75% chance of winning would be –300 (75 divided by 25), which makes sense, as you should have to pay $300 to win $100 if you have a 75% chance of winning. An 80% chance of winning would equal a line of –400 (80 divided by 20) and so on.

These are lines without juice, of course. If a team has a 75% chance of winning and the true accurate line should be –300, more likely you’ll see this team at –330 and the underdog at +270. So if you meet the two lines in the middle, you should get the true (no vig) line of –300.

To complicate matters further, sports books don’t necessarily split the lines right down the middle. Books play games with lines to attract action on one side. Perhaps they have too many bets on the favorite and want to balance it a bit and reduce their exposure. So for a line with a true value of –300, they could make the favorite –350 and the underdog +290; this invites action on the underdog, as all other books in town or online are offering +270. Bettors will like this number, even though they’re still at a slight disadvantage (recall the true line is +300).