Introduction

The global soccer betting market is a high-volume predictive system, where bookmakers generate and update millions of probability estimates in real time. But how accurate are these predictions and how do different bookmakers stack up against each other?

To explore these questions, I’ve collected a dataset of over 250 million betting lines from 1.25 million soccer fixtures worldwide, spanning multiple years, leagues, and market types. This gives us a unique dataset to evaluate bookmaker performance on a large scale.

For this article, I’ll be narrowing the focus to just the major European leagues and analyzing the moneyline (1X2) markets - the outcome of the match: home win, draw, or away win.

We'll be digging into:

• Overrounds and how bookmakers build in margin
• Bookmaker accuracy using Ranked Probability Scores (RPS)
• Calibration curves to test how well odds translate to real-world outcomes

What Is the Overround?

In any betting market, the overround is the bookmaker’s built-in profit margin. This is the amount by which the implied probabilities of all outcomes exceed 100%.

For example, in a simple 3-way soccer market (Home Win / Draw / Away Win), the odds might be:

• Home Win: 2.00
• Draw: 3.60
• Away Win: 3.60

To convert these odds into implied probabilities, we take the inverse:

• Home Win: 1 / 2.00 = 0.500
• Draw: 1 / 3.60 ≈ 0.278
• Away Win: 1 / 3.60 ≈ 0.278
• Total: 0.500 + 0.278 + 0.278 = 1.056, or 105.6%

That extra 5.6% is the overround, or the bookmaker’s edge. In a perfectly fair market with no margin, the total implied probabilities would sum to 100%.

Overrounds by Competition and Season

The table below shows average overrounds for moneyline (1X2) markets across the major European leagues, broken down by season. Several patterns stand out immediately:

Top-tier leagues like the Premier League, La Liga, Serie A, and the Bundesliga consistently have the lowest overrounds - typically between 4.1% and 5.1%. These markets are the most competitive, liquid, and efficient, so bookmakers tend to apply tighter margins.

Second divisions and lower leagues, such as League One, Serie B, or La Liga 2, often feature significantly higher overrounds, often pushing 7% or more. These markets may be less efficient and attract less volume, giving bookmakers more pricing power.

Also, there’s been a noticeable upward trend in overrounds over time across most competitions. For example:

• The Premier League has crept from 4.12% to 4.65% over five seasons.
• Serie B rose from 6.51% to 7.18%.
• La Liga 2 shows a particularly sharp increase: 6.77% to 7.59%.

Table 1: Overrounds by Competition and Season

Premier League Overrounds by Bookmaker

Zooming in on the English Premier League, we can see clear differences in how various bookmakers price their moneyline markets. Table two below shows average overrounds for each bookmaker over the last five seasons.

Several key themes emerge:

• Pinnacle consistently has the lowest overrounds, averaging between 2.39% and 3.00%. This aligns with Pinnacle’s reputation as a low-margin, high-volume bookmaker that attracts sharper bettors. Their pricing reflects high market efficiency.
• 1xBet and Unibet also offer relatively tight margins, typically under 3%, though Unibet shows a notable spike in 2024/2025, possibly indicating a change in pricing strategy.
• Mainstream bookmakers like bet365, bwin, and William Hill tend to operate with higher overrounds, often between 5% and 6%, with William Hill even reaching 7.32% in 2023/2024. These firms serve a broader customer base and tend to target recreational bettors.
• 888sport, Betfair, and Betway show a trend of steadily increasing margins over the seasons, suggesting a shift toward more conservative pricing.
• 10bet jumps dramatically to 6.18% in 2024/2025 from a relatively sharp 3.78%, suggesting a drastic repositioning of itself in the market.

When we break down overrounds in the Premier League by bookmaker, a clear divide emerges between two groups:

• Low-margin operators like Pinnacle and 1xBet, which consistently offer tighter pricing.
• Mainstream bookmakers such as William Hill, bet365, and bwin, which price with significantly higher margins.

This split reflects two fundamentally different business models:

Mainstream bookmakers like William Hill, bet365, and bwin typically operate with overrounds in the 5–7% range. These firms primarily cater to recreational bettors - users who are betting more for entertainment than profit. Many of these customers are less likely to shop around for better odds or understand how bookmaker margin erodes long-term returns. As such, these bookmakers can afford to be less competitive on price, and may even benefit from it since tighter pricing can attract sharp bettors they’d rather avoid.

In contrast, low-margin operators such as Pinnacle or 1xBet attract price-sensitive or professional bettors. Their overrounds often sit below 3%, even in top-tier markets. These firms rely on a volume-based model, welcoming sharp action and managing risk through efficient pricing and faster line movement, rather than blocking or limiting users.

Table 2: Premier League Overrounds by Bookmaker

Bookmaker Accuracy by League: Ranked Probability Scores

To evaluate how well bookmaker odds align with actual match outcomes, we use the Ranked Probability Score (RPS) - a strictly proper scoring rule that measures the accuracy of probabilistic forecasts across ordered outcomes (like home/draw/away in football). Lower values indicate better predictive performance, with perfect accuracy scoring 0.

Table 3 below shows average RPS values for moneyline markets across major European leagues, broken down by season:

Several key observations stand out:

• Top-tier leagues tend to have lower RPS values, indicating more accurate and better-calibrated odds. For example:
  • The Netherlands' Eredivisie, Portugal’s Liga Portugal, and Italy’s Serie A consistently sit at the top of the accuracy table, with RPS scores as low as 0.175–0.185.
  • The Premier League, La Liga, and Bundesliga also show strong performance, generally ranging between 0.18 and 0.20.
• In contrast, lower-tier leagues such as England’s League One/Two, Serie B, and La Liga 2, tend to produce higher RPS scores, often above 0.21, suggesting greater uncertainty and less precise odds.
• Accuracy varies season-to-season within leagues, but not that wildly, suggesting relative stability in how bookmakers price different competitions. Some leagues (like France's Ligue 1) show very consistent RPS values year over year.

Table 3: Bookmaker Accuracy by League: Ranked Probability Scores

Accuracy by Bookmaker: RPS in the Premier League

Having seen how bookmaker margins differ, it’s natural to ask: Do tighter margins translate to more accurate odds? One way to answer that is by comparing Ranked Probability Scores (RPS) across bookmakers in the Premier League.

At first glance, the differences in RPS are remarkably narrow, typically falling between 0.18 and 0.20 across seasons. That’s perhaps expected in a highly liquid, competitive market like the Premier League, where bookmakers converge on efficient prices.

Still, some patterns emerge:

• No clear link between margin and accuracy: Despite having the lowest overrounds, Pinnacle does not clearly outperform higher-margin books like William Hill or bet365 in terms of RPS. In fact, William Hill occasionally posts the lowest (i.e., best) RPS, such as 0.188 in 2021/2022. This supports the idea that bookmaker margin and forecast accuracy are not tightly correlated. Higher-margin books may simply be padding prices, not offering worse forecasts.
• 1xBet, Betway, and Pinnacle show near-identical performance, suggesting they may be operating with similar models or reacting similarly to market movement.

So while Pinnacle leads on pricing (low overround), and books like William Hill apply large margins, there’s no strong evidence here that sharp-friendly books are forecasting significantly better, at least not when measured by RPS alone in the Premier League.

Table 4: Accuracy by Bookmaker: RPS in the Premier League

Are Bookmakers Well-Calibrated?

A final test of accuracy is calibration: how well do predicted probabilities match observed outcomes? If a bookmaker assigns a 70% probability to an outcome, that outcome should occur roughly 70% of the time for the model to be considered well-calibrated.

The plot below shows calibration curves for bookmaker probabilities across home wins, draws, and away wins. The dashed black line represents perfect calibration where predicted probability equals observed frequency.

The results are impressive:

• All three outcome types - Home Win, Draw, and Away Win - track the diagonal line closely, indicating that bookmakers’ odds are well-calibrated overall.
• There's no major systematic bias: bookmakers aren't consistently under- or overestimating the likelihood of any specific outcome across probability ranges.
• Deviations are small and mostly in the extremes, where data can be noisier due to fewer data points.

Taken together with the low RPS scores in previous sections, this reinforces a key conclusion:

Bookmakers aren’t just padding prices, their forecasts are statistically sound and well-aligned with real-world outcomes, especially in major markets like the Premier League.

Plot 1: Calibration Curves for Bookmaker Probabilities

Beating the Bookmaker in Obscure Leagues?

A common belief among many bettors is that focusing on lower-profile leagues, where information is scarce, offers an edge. The logic is simple: if you know more than the bookmaker, you can find value. However, the data tells a more cautionary story.

Let's take the Seychelles and Mongolian Premier Leagues as examples:

• Seychelles Premier League: Overround = 9.76%
• Mongolia Premier League: Overround = 12.03%

These are massive compared to the 4-5% typical in top European leagues. But high margins alone don’t mean sloppy forecasts. In fact, the RPS scores tell a different story:

• Seychelles RPS = 0.230
• Mongolia RPS = 0.192

Mongolia, in particular, is priced as accurately as many major European leagues despite the bookmaker charging a hefty margin. Even Seychelles, with a worse RPS, still falls within the range seen in many second-tier European competitions.

So while obscure leagues may feel like an edge, the data suggests bookmakers are doing a surprisingly good job and charging extra for the uncertainty.

If anything, the takeaway is this: the more obscure the league, the higher the margin - not necessarily the worse the forecast. Bookmakers are aware of their informational disadvantage and price accordingly to protect themselves. You’re not beating the market by knowing more about Tuv Azarganuud's starting XI but you are paying a premium for the privilege of trying.

Conclusion

Across millions of betting lines, one thing is clear: bookmakers, especially in major markets, are very good at what they do. Their odds are well-calibrated, their forecasts consistently accurate, and their margins finely tuned to the level of competition and market liquidity. Even in obscure leagues, they’re cautious but not careless.

But that doesn’t mean the market is unbeatable. If anything, it shows that finding an edge requires more than intuition - it demands scale, rigor, and nuance. That’s exactly what a data-driven approach is designed to uncover.

Whether you're looking to evaluate specific bookmakers, spot outliers, or understand where pricing deviates from probability, I’ll be continuing to dig into this dataset and sharing anything interesting I find.

For those looking for signal in a noisy market, I hope this is an interesting start.