Why Do Betting Odds Move – And Who Controls Them?

Before diving into the details, it’s important to understand one thing: betting odds are not just numbers based on statistics. They are a constantly updating reflection of probability, market behaviour, expert insight, and the bookmaker’s need to protect their profit margin. Below is how each of these factors works together to create the odds you see on your screen.

The top betting sites generate their odds using a combination of data-driven methods and expert analysis. Their goal is to offer fair and accurate prices for every market, built around the true probability of each outcome occurring.

Recent history, head-to-head records, data analysis, external factors and the opinion of experts all factor into a bookmaker's opening odds and the odds right until the closing line. Let’s take a look at the process behind the numbers and how the bookmakers are setting betting odds.

Types of Odds Used by Bookmakers

Before analysing how odds are created, it’s useful to understand the three main formats:

• Decimal odds (3.0, 1.85) – common in Europe; show total return per 1 unit.
• Fractional odds (2/1, 5/2) – used in the UK; show profit relative to stake.
• American odds (+150, -120) – popular in the US; positive values show how much you win with a 100-unit stake, negative values show how much you need to bet to win 100.

Regardless of format, all odds express the same thing: implied probability.

Data Analysis

The most obvious factor behind the betting numbers is the analysis of all the data available. This will look at all historical data of head-to-head records, individual performances, team performances, recent form and more.

The team employed by bookmakers use advanced algorithms to analyse all the data that is available that relates to the market in question. The factors considered will eventually estimate the true probability of the market's outcome, which dives deep into the above-mentioned factors.

For example, if Harry Kane - an elite goal scorer in top form - is playing for the favoured England against an out-of-form team like San Marino, the bookmakers will factor in his previous form against them, the terrible form of San Marino in years gone by and Kane's overall goalscoring for England.

Team and Player Performance

Another obvious factor that bookmakers consider is the form of the team and performance, regardless of their history against an opponent.

For example, Andy Murray’s form against the likes of Novak Djokovic prior to his 2012 Wimbledon win was quite poor. However, after a sensational few years of winning form, Murray would have seen his odds cut and closer to becoming the favourite than ever before in a match between the two.

As the years went on, injuries and bad form hampered Murray’s career, and meetings with players like Djokovic towards the end of his career would have become much larger.

The Market Response to Bettors

What bettors are betting on massively impacts the odds bookmakers make.

Bookmakers will open up with what is known as ‘opening odds’. These odds will be determined based on an initial assumption of an outcome, external factors like the weather and injuries, as well as any data available.

Over time, up until the closing odds before the event begins, the odds are likely to fluctuate based on the factors mentioned in their data analysis. However, what also greatly impacts the betting odds is the market responding to what is being betted on.

For example, if one team is priced at 2/1 (3.0) at the opening odds, but the public bets a lot of money on this market with the idea that it will win, bookmakers are likely to decrease these odds as a response. This will also impact the other teams' odds, and many other markets within that event, such as points/goals scored and so on.

How and Why Lines Move

A sudden shift in odds is called a line movement. This usually happens when a large amount of money is placed in a short period of time, often from sharp bettors. For example, if Liverpool open at 2.10 to win and a professional bettor places a large stake based on insider-level analysis, the bookmaker may instantly drop the odds to 1.95 or lower to balance their risk. Public money can also move lines, but sharp money usually triggers the fastest and most aggressive changes.

So, if you want to get the best odds, keep an eye on the opening odds, how they change, and the closing odds right before the event starts, as what others are betting on will impact the odds you will get.

Expert Opinions

Although this won’t deter a bookmaker from the crucial data analysis too much, the opinions of experts in the field will impact the odds, to an extent. This goes for both non-bettors and ex-professionals in a sport, as well as expert bettors who make a living out of gambling on the odds provided.

Similar to the market responding to what is betted on, the opinion of expert bettors will impact the odds. This comes down to the simple factor of how a professional bettor is often correct, watches the market all the time, and ultimately determines the most probable outcome.

Ex-professionals in the field could also have an impact on the process behind the numbers with what they’re saying, but expert bettors and what they are concluding is more important to the bookmaker, due to their expert analysis of data.

Sharp Money vs. Public Money

Bookmakers treat different types of bettors differently.

• Public money comes from casual bettors who tend to follow hype, big names, or recent results.
• Sharp money comes from professional bettors with proven profitable histories.

When sharp money enters the market, bookmakers adjust quickly because these bettors are statistically far more accurate. Public money influences odds too, but usually slower and on high-profile matches where a large number of recreational bets accumulate.

Any External Factors

Factors that may not come into the consideration of the casual bettor are the external factors that could impact a market. For example, the weather could impact one player/team, in contrast to another. The away/home form of a team/player could have a say too, while suspensions and injuries are a massive factor in determining odds.

An injury to a key player in a team no doubt changes the odds, such as if Manchester City were to lose Erling Haaland for a game. Furthermore, a player coming back from an injury and perhaps not at 100% will also impact the odds you can bet on.

Real-Time Updates

This area of the process behind determining the numbers relates to in-play/live betting, as opposed to the odds before the event has started.

For example, injuries and red cards within a game of football or rugby will change the odds, as one team may have become weaker as a result. As well as this, shifts in momentum in defence and attack will change the odds, such as if one team is facing a lot of attempts to score from the opposition.

The Bookmakers Wanting to Make a Profit

It goes without saying, but the bookmakers create odds with one goal in mind: making a profit.

Indeed, they will, in most cases, favour one team/player to win more than another, but the bookmaker will set built-in margins and calculate the odds to such an extent in order to ensure they make a profit on, no matter the result of a sporting event.

The Overround: How Bookmakers Build a Margin Into the Odds

Even when bookmakers publish “fair” odds, a built-in margin always exists. This margin is known as the overround and guarantees the bookmaker profits in the long run. For example, if a match should statistically have a 50%–50% probability, the true decimal odds would be 2.00 on each team. Instead, a bookmaker might offer 1.91 vs 1.91, ensuring that no matter how people bet, the total implied probability exceeds 100%. This overround is why long-term profitability is so difficult for casual bettors and why bookmakers stay consistently profitable.

This is another reason why you can bet on more than just the outright winner of a sporting event and have the chance to bet on player/team props and more markets within an event.

Final Thoughts

Bookmaker odds are the end result of probability models, expert insights, real-time market behaviour, and a built-in margin that protects the bookmaker’s profitability. Understanding how these elements work together helps bettors recognise why odds move, when value appears, and how markets behave long before a match even begins.