What is Overround?
Overround (also called the bookmaker’s margin) is how a bookmaker builds profit into their odds. It’s the total of all the implied probabilities for every possible outcome of an event. If the odds were perfectly fair, this total would equal 100%. Anything above 100% represents the bookmaker’s built-in edge — their guaranteed profit over time.
If the total exceeds 100%, the excess represents the bookmaker’s profit margin.
In an ideal, fair market, the total of all outcomes would equal exactly 100%, so neither side has an advantage. Bookmakers add a margin above this so they can guarantee long-term profit.
How to calculate Overround
Here’s how to calculate it:
- Convert each outcome’s odds into implied probability using this formula:
Implied Probability = 1Decimal Odds
- Add up all the implied probabilities for every possible outcome of the event.
- Calculate the overround by subtracting 100% from the total implied probability sum:
- Overround = (Total Implied Probability−1) × 100%
Example: Football match: Arsenal vs Chelsea
Outcome | Decimal odds | Implied probability |
|---|---|---|
Arsenal to win | 2.10 | 47.6% |
Chelsea to win | 3.40 | 29.4% |
Draw | 3.60 | 27.8% |
Total: 47.6% + 29.4% + 27.8% = 104.8%
Overround = 104.8% − 100% = 4.8%
This market has an overround of 4.8%, meaning the bookmaker has a 4.8% built-in edge.
Typical Overround ranges in different markets
Market Type | Typical Overround | Notes |
|---|---|---|
Major football leagues | 102–104% | Highly efficient, low-margin markets |
Tennis matches | 103–105% | Two outcomes, often sharp |
Niche sports / lower leagues | 107–110% | Less liquidity, higher margin |
Accumulators | 115%+ | Margins compound across selections |
Why understanding overrounds matters
- Reveals the bookmaker’s margin: A higher overround means a bigger built-in profit for the bookmaker. It shows how much each market is weighted in their favour.
- Highlights real value: Lower overrounds (closer to 100%) usually offer fairer odds and better long-term returns.
- Helps compare bookmakers: Sites like Pinnacle and Betfair Exchange typically run lower overrounds, helping you find the most competitive odds.
- Indicates market efficiency: Big events like Premier League matches have tighter overrounds, while niche markets show higher ones, and more inefficiencies.
Supports long-term strategy: Tracking overrounds helps you avoid overpriced markets and build a value-driven betting approach.
How to find lower overrounds
1. Compare odds across multiple bookmakers
The simplest way to spot low overrounds is by comparing prices for the same event on different sites. Higher odds on the same selection usually indicate a smaller margin.
2. Focus on major markets
Popular events, like Premier League football, ATP tennis, or Champions League matches, tend to have high liquidity and smaller overrounds due to strong competition between bookmakers.
3. Avoid obscure or low-liquidity events
Niche sports, minor leagues, or novelty markets often have wider margins. Stick to mainstream competitions if you want tighter pricing.
4. Look for exchanges and sharp books
Betting exchanges and sharp bookmakers usually operate with minimal margins, offering closer-to-fair prices.
5. Track overrounds over time
Regularly check how overrounds fluctuate across markets and bookmakers. This helps you spot consistent value sources and avoid overpriced odds.
How sharp bettors use Overround to their advantage
- They hunt for low-margin markets. Professionals target events where the total implied probability sits close to 100%. These low-overround markets leave less room for bookmaker profit, and more room for genuine value.
- They exploit inefficiencies. When a market’s overround is high, it usually hides poor pricing. Sharps analyse those numbers to uncover outcomes where the bookmaker has overadjusted, creating positive expected value (EV) opportunities.
- They strip out the vig. By removing the bookmaker’s margin (“de-vigging” the odds), they calculate true implied probabilities and compare them to their own models or data. This reveals whether a price is actually worth backing.
- They benchmark bookmaker sharpness. Consistently low overrounds signal a sharper, more efficient bookmaker. Sharps use this to decide where to place bets, and which books to fade when prices diverge.
They refine long-term strategy. Tracking overround patterns helps bettors measure where they’re consistently finding value and which markets to prioritise. Over time, this transforms overround analysis from a concept into a measurable edge.
Conclusion
Overround is the bookmaker’s built-in profit margin, but understanding it gives bettors a crucial edge. Knowing how to calculate and interpret overround helps you spot value, compare bookmaker fairness, and avoid overpriced markets. This simple concept has powerful implications, allowing you to make smarter, more strategic bets based on insight rather than luck.
Frequently asked questions
Can Overround change between bookmakers?
Yes. Each bookmaker sets their own margins, so overrounds vary. Comparing them can reveal which bookies offer the most competitive prices. Shopping around for lower overrounds can improve your long-term returns.
Do exchanges have Overround too?
Betting exchanges usually have much lower overrounds because they charge a small commission instead of building profit into the odds. This makes exchanges a popular choice for bettors seeking fairer prices.
Is a low Overround always better?
Usually, yes, but it depends on the market. A low overround indicates fairer odds and better value, though it also reflects a more efficient market, meaning price inefficiencies are less common.
How can I calculate fair odds by removing the Overround?
Divide each implied probability by the total of all probabilities, then convert them back into decimal odds. This reveals the true market prices without the bookmaker’s margin.
Why do accumulators have higher Overrounds?
Each leg adds its own margin, so overrounds compound across selections. More legs mean a larger bookmaker edge, even if payouts appear higher.