What Is the Run Line in Baseball Betting?

The baseball run line is the line that a bettor will use to determine whether or not to wager on a game. The concept behind the run line is very simple – identify the statistical factors that influence the outcome of a game and then use those statistics to create a betting line for that game. The general guideline is to avoid betting on games where the run line is 1 or 2 and instead favor those games where the run line is more in the 3.5 to 4.5 range.

What Does the Run Line Mean?

A few things, actually. First, the run line effectively determines the over/under for the game based on the betting public’s implied perception of how the game will play out. Second, it is an indication of whether or not to value a team’s current form or future performance when determining a wagering interest. A team with a strong record usually draws a larger wagering pool due to its popularity, and similarly, a team in poor form or with large fluctuations in performance might also see a decline in interest. Third, the run line can be used to identify a game’s true outcome because as the saying goes, statistics don’t lie. However, there are exceptions to this general rule and sometimes statistics can be misleading. Last but not least, the run line can be a good starting point for the construction of winning wagers because most people agree that games with a high degree of difficulty usually have a low percentage of wins.

How Does One Calculate The Run Line?

The run line is usually calculated using some variant of the following formula:

  • Odds of winning (over/under)
  • Current winning percentage
  • Inning number
  • Weather conditions
  • Division
  • Cumulative home score
  • Cumulative away score
  • Total run score
  • Estimated length of game
  • Under/over

The formula is designed to take into account all the important factors that can affect the outcome of a game and subsequently the run line for that game. If you aren’t sure how to calculate the run line or any of the other variables used in the formula, don’t worry – we’ll go over each one in turn.

Odds of Winning

The first step in calculating the run line is determining the odds of winning for both teams. As it happens, most sportsbooks offer odds for a large number of games, so odds are typically easy to locate. Once you have those, you can plug them into the following formula to determine the effective over/under for the game:

  • Odds of winning (over/under)

Odds of winning are effectively the odds of the game, adjusted for parlay odds and betting limits. You won’t need to look any further for your first variable in the formula – odds of winning are always a part of the equation. In the United States, odds of winning are normally calculated using the following formula:

  • Home team odds
  • Away team odds
  • (Visitor count if inside park)
  • (Home team total score)
  • (Away team total score)

Current Winning Percentage

The second variable in the equation is the current winning percentage for the team(s) you are analyzing. Like the odds of winning, this figure is easy to obtain because most sportsbooks keep track of their winning percentage for all their games and display it in a handy format on their websites. Simply find the team you are interested in analyzing and then enter their winning percentage from the previous year or most recent 6 games (whichever is applicable). You can also click here to see the Seattle Mariners current winning percentage in more detail.

You can use any of the following forms to enter winning percentage data:

  • Most recent winning percentage
  • Winning percentage for the previous year
  • Home vs. Away splits
  • Averages of previous seasons
  • Most recent 6-game winning streak
  • Most recent 12-game winning streak
  • Most recent 20-game winning streak

Inning Number

The third variable in the equation is the number of innings the game will last. This is typically given as 1, 2, or 3 because the game length will vary depending on the time of day, day of week, temperature, and a few other factors. For instance, Thursday night games are typically shorter than Saturday afternoon games, and so on. You won’t need to worry about varying game lengths too much because most online sportsbooks offer all the major baseball games as either 3 or 4 innings or as full innings.

Weather Conditions

The next step in the equation is to consider the weather conditions specific to the date and location of the game. This is mostly applied to outdoor sports because weather conditions can have a significant effect on the outcome of a baseball game played under regular circumstances. For instance, it is well known that baseball games are usually played in the winter and that weather conditions will affect a team’s performance. Rain disrupts the game, making it nearly impossible for the pitcher to locate the zone, and so forth. If possible, you should always check the weather conditions before the game especially if you are traveling a significant distance to attend the game.

There are a few different formulas that one can use to calculate the odds of winning based on weather conditions. One of the most popular ones is the following:

  • Home team win if temperature is 64 degrees or greater
  • Home team win if temperature is below 64 degrees
  • Either team win if temperature is between 45 degrees and 63 degrees
  • Away team win if temperature is below 45 degrees
  • Either team win if temperature is between 35 degrees and 44 degrees
  • Home team win if temperature is 35 degrees or greater
  • Home team win if temperature is below 35 degrees
  • Either team win if temperature is between 22 degrees and 34 degrees
  • Away team win if temperature is below 22 degrees

In this formula, the variables are the home team’s temperature and the visitor’s temperature. As you would expect, the higher the home team’s temperature, the better the chance of winning. Similarly, the worse the weather conditions, the worse the team’s chance of winning. However, there is also another significant factor at play here: the warmer the weather, the more likely it is that the ball will play slightly better due to increased air pressure. This increased air pressure makes it easier for the players to grip the ball – especially on long drives to right field.


The fourth variable in the equation is the division of the teams you are analyzing. If you are analyzing the Cubs and Cardinals, for example, you would want to include the Cubs’ current standing relative to the Cardinals in this calculation. You can use any of the following forms to enter division data:

  • Series record against common opponent
  • Most wins vs. common opponent
  • Head-to-head record (if applicable)
  • Divisional round (if applicable)
  • Season standings (if applicable)
  • (Visitor count if inside park)
  • (Home team total score)
  • (Away team total score)
  • (Home team winning percentage)
  • (Away team winning percentage)
  • (Home vs. Away record)
  • (Games played at home)
  • (Games played away)

The above variables are all things that you can use to calculate the effective over/under for the game. It is not meant to be an all-inclusive formula because there are many other factors that could affect the outcome of a game. Ultimately, you will have to decide what is the most significant factor for your own personal use. In the United States, baseball odds are typically posted daily on websites such as OddsShark.com and SportsBettingReview.com and the public typically has access to this information 24/7.