What Is Overround In Horse Racing 

 June 26, 2023

By  Philip Borrowman

One factor that most casual observers may overlook but is of central importance to bettors and bookmakers alike is the concept of 'Overround'.

But what is overround in horse racing, and why does it matter? If you've ever asked yourself this question, you're in the right place. This blog post aims to unravel the mysteries surrounding overround, illustrating its importance in the betting landscape of horse racing.

Before we delve into the detailed explanation, let's start with a basic understanding.

The term 'Overround' is a fundamental concept in betting that refers to the built-in profit margin bookmakers employ to ensure they remain profitable. 

This is essentially what allows bookmakers to stay in business regardless of the race's outcome. Sounds intriguing, right?

Stay tuned as we discuss its calculation, its impact on punters and bookmakers, and why it's a critical concept that can enhance your horse racing betting strategies.

Understanding the overround can empower you to make more informed decisions in your betting endeavors, and potentially increase your returns over time. Let's dive in!

Deep Dive into Overround

Detailed definition of Overround

The term 'Overround' might sound complex, but its core concept is straightforward. Also known as the 'vig', 'juice', 'margin', or 'the cut', the overround refers to the combined market percentage of all probable outcomes exceeding 100%. 

This percentage exceeding 100% is the bookmaker's mathematical advantage, ensuring they remain profitable regardless of the race's outcome.

How Overround works in horse racing

In horse racing, the overround is subtly tucked into the odds offered on each horse.

Bookmakers carefully set these odds to guarantee that, in total, they sum to more than a 100% probability.

This might sound odd as the sum of all probabilities in an event should technically equal 100%. However, the 'extra' that surpasses 100% is the overround.

For example, in a race with three horses where each is given an equal chance of winning, a 'fair book' would present odds of 2/1 for each horse.

These odds equate to a 33.33% implied probability of winning for each horse, summing up to exactly 100% for all three horses. However, to create an overround, a bookmaker may offer odds of 1/1 (or 'even money') on each horse.

This equates to an implied probability of 50% per horse, leading to a total of 150% for all three horses, with the 50% surplus serving as the overround.

Explanation of why Overround is important in horse racing betting

Firstly, it helps bettors comprehend how bookmakers make a profit, leading to a better understanding of how the betting system works.

Secondly, understanding the overround can also give bettors insights into the potential profitability of a particular set of odds.

In general, a lower overround signifies a better deal for bettors as it means the bookmaker is taking a smaller cut.

Conversely, a higher overround implies the bookmaker is taking a larger slice, making it harder for bettors to turn a profit in the long run.

Hence, gaining a clear understanding of overround in horse racing betting is an essential step towards honing your betting strategy and improving your returns.

Calculation of Overround

To bring a practical understanding of this concept, let's look at how overround is calculated.

The first step is to convert the betting odds for each horse into their implied probability.

The formula for this conversion is:

  • Implied Probability = 1 / Decimal Odds

Once we have the implied probabilities for all horses, we sum these probabilities. If the total exceeds 100%, the surplus is the overround.

Examples of Overround calculations with different sets of odds

Let's take an example of a horse race with three horses - A, B, and C. The bookmaker has given decimal odds of 2.0 for horse A, 3.0 for horse B, and 4.0 for horse C to win the race.

Here's how we calculate:

Convert the odds into probabilities:

  • Horse A's implied probability = 1 / 2.0 = 0.50 or 50%
  • Horse B's implied probability = 1 / 3.0 = 0.33 or 33%
  • Horse C's implied probability = 1 / 4.0 = 0.25 or 25%
  • Add all these probabilities:
  • Total probability = 50% + 33% + 25% = 108%

In this scenario, the overround is 8%, representing the bookmaker's profit margin.

Importance of the Overround calculation in determining the potential outcome

The Overround calculation is key to understanding the potential profitability of a given set of odds. As a bettor, this helps you identify whether you're getting good value for your bets.

Markets with a low overround typically provide better value since the bookmaker's cut is smaller. In contrast, a high overround means the bookmaker is taking a larger cut, reducing potential profitability for bettors.

By making calculations part of your betting strategy, you can make more informed decisions on where to place your bets.

It can also help you identify when odds might be skewed in favor of or against certain outcomes, providing further insights for your betting strategy.

Overround's Impact on Punters

Understanding how Overround affects the punter's profits

It's clear that overround is the bookmaker's best friend, as it guarantees them a profit over time. But for the punter, it presents a significant obstacle to making consistent profits from betting.

Essentially, the overround acts as a tax on bets, with a higher overround equating to a larger 'tax rate'.

The impact of the overround is often overlooked in the short term, especially when a punter has a successful day at the races.

However, in the long term, its effect becomes more apparent as it gradually erodes the potential profits a bettor can make.

Strategies to combat or mitigate the impact of the Overround

So, how can punters combat or at least mitigate the impact of the overround?

One straightforward approach is to shop around for the best odds.

Different bookmakers will have different overrounds for the same race, so taking the time to compare odds can be well worth it.

Another strategy is to look into betting exchanges. Unlike traditional bookmakers, betting exchanges allow punters to bet against each other. The overround is generally lower on these platforms as they earn their profits through commission on winning bets instead of building in an overround.

Explanation of how to identify and exploit situations where the Overround is less than 100%

Occasionally, due to competition between bookmakers or errors in pricing, situations may arise where the overround is less than 100%.

This situation is known as an 'underround'. When this occurs, it's possible for a punter to guarantee a profit by placing the right bets with different bookmakers - a practice known as 'arbitrage betting'.

However, it's worth noting that these situations are rare and often corrected quickly by bookmakers. Plus, some bookmakers frown upon arbitrage betting and may limit or close the accounts of those they suspect of engaging in this practice.

Despite these challenges, staying aware of the overround can help punters spot such opportunities and potentially benefit from them.

Overround from the Perspective of Bookmakers

Explanation of how bookmakers use the Overround to ensure a profit

From the perspective of the bookmaker, the overround is a fundamental tool for risk management.

By setting their prices so that the total implied probability exceeds 100%, bookmakers create a situation where they expect to make a profit regardless of the outcome.

Essentially, the overround ensures that the sum of money they pay out to those who make winning bets is less than the total amount of money wagered.

Importance of the Overround for the stability and sustainability of the betting market

The overround is crucial to the stability and sustainability of the betting market. Without it, bookmakers would be much more vulnerable to big losses.

This could put bookmakers at risk of going out of business, which would significantly reduce competition in the betting market, leading to less favorable odds for punters.

Hence, while it might seem like the overround is only there to the detriment of bettors, it's also a key factor that allows the betting market to exist in its current form.

Balancing bettor interest and bookmaker profit

Bookmakers have to walk a fine line when setting the overround. On one hand, a higher overround increases their potential profit and reduces their risk.

On the other hand, if their overround is significantly higher than their competitors', bettors may take their business elsewhere. Therefore, bookmakers must balance their need to make a profit and cover their risk with the need to offer attractive odds to their customers.

In conclusion, while the overround is often seen as the enemy of the bettor, it's important to remember that it also plays a crucial role in the functioning of the betting market.

By understanding what the overround is and how it works, both bettors and bookmakers can make more informed decisions and potentially increase their profits.

Summary & References

Recap of the importance and impact of Overround in horse racing

Throughout this article, we have uncovered the intricacies of the overround, an underappreciated yet fundamental aspect of horse racing betting.

This concept, buried within the betting odds offered by bookmakers, reveals the bookmaker's built-in profit margin and the strategies they use to ensure a profit no matter the race's outcome.

Final thoughts on the strategic application of understanding Overround for both punters and bookmakers

For punters, understanding the overround illuminates the path to more strategic betting. It sheds light on the importance of comparing odds, seeking out lower overrounds, and even exploiting rare underround opportunities.

For bookmakers, the overround is a critical risk management tool, allowing them to strike a delicate balance between making a profit and offering competitive odds.

Encouragement for readers to apply their newfound understanding of Overround in their betting strategies

So, "What is overround in horse racing?" is a question with an answer that takes us into the heart of betting strategy and market dynamics.

We encourage all readers, whether you're a punter seeking an edge or a curious observer of horse racing, to apply this newfound understanding of overround in your interactions with this thrilling sport.

It's not just about picking the winning horse; it's about understanding the field and making smart, informed decisions that heighten your engagement with horse racing.

By understanding the overround and the mathematics behind betting, you're better equipped to navigate the exciting world of horse racing betting.

Happy betting and good luck!

Philip Borrowman


I am a full-time marketer and part-time Betfair trader. I have over 10 years of experience in the pre-race and in-play horse trading markets and spend my days writing guides, tips and tricks to help beginner Betfair traders find their way to a profitable second income. Read my story of trading on Betfair.

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