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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsSports betting apps do not share one universal odds formula. A displayed price is the end point of a chain: someone estimates how likely an outcome is, that estimate is converted into odds, and the operator then adds a margin and applies its own risk controls. Some operators build those estimates in-house, while many draw on data providers. Live markets and combined bets add two more steps: updating prices as the event unfolds, and accounting for outcomes that move together. The sections below follow that chain using documented examples from Betfair and Sportradar, and they flag where those examples stop applying.
What an odds number encodes
Odds are a way of writing a payout and a probability in the same number. Betfair’s customer guide converts fractional 9/1 into a 10% implied chance. The same price in decimal format is 10.00, because decimal odds include the returned stake: a 1-unit stake returns 10 units in total, of which 9 units is profit.
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| Format | Example price | What a 1-unit stake returns | Implied probability |
|---|---|---|---|
| Fractional | 9/1 | 9 units profit plus the 1-unit stake back | 10% (1 ÷ (9 + 1)) |
| Decimal | 10.00 | 10 units total, stake included | 10% (1 ÷ 10.00) |
Implied probability is a way of reading the price. A 10% reading tells you what chance the odds assume; it does not prove the event has a 10% chance in the real world. An operator’s price can be too high or too low relative to the true likelihood, and that gap is where the operator’s margin and any mispricing sit.
A representative pricing path
Sportradar’s Unified Odds Feed documentation describes one method for building a price: estimate whether selections are correlated, combine their probabilities, convert the result into fair odds, and then apply a margin to produce the offered odds. This is a documented example, not a description of every sportsbook’s process. It is most clearly illustrated with bet builders and combined markets, but the same logic underlies single-market pricing.
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Step 1: Decide whether the selections are independent
The first question is whether one outcome changes the chance of another. Two results with no connection, such as the winner of one match and the winner of an unrelated match, can be treated as independent. Two results in the same game, such as a team winning and that team’s star scoring, are often linked. If the pricing model ignores that link, the combined price will be wrong in one direction or the other.
Step 2: Combine the probabilities
For independent selections, the combined probability is the product of the individual probabilities. For correlated selections, the model applies a correlation adjustment, so the joint probability can be higher or lower than the simple product. Sportradar’s documentation says its Bet Builder prices correlated selections, which is the reason a bet builder cannot be priced by multiplying the decimal odds of each leg.
Step 3: Convert the probability into fair odds
Fair odds are the reciprocal of the combined probability, with no margin built in. Sportradar describes its Fair Odds product as a margin-free baseline. An operator can then decide how much margin to overlay on that baseline.
Step 4: Apply the margin to produce offered odds
The final step is the one most readers see. Sportradar’s documentation states the principle directly:
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“Finally, a margin is added on top of the fair odds to generate the final odds offered.”
Sportradar Unified Odds Feed customer documentation, “Odds & Margins”
The sources reviewed for this article do not specify how an operator divides its margin across outcomes or markets, so the example below uses a simple, hypothetical adjustment to show the effect rather than any operator’s actual figures.
A worked example with illustrative numbers
Take a two-outcome market where each side has a 50% fair probability. Fair decimal odds are 2.00 on each side, and the implied probabilities add up to 100%. Now assume the operator shortens each price to 1.90. The effect on the book is visible when you add the implied probabilities together:
| Outcome | Fair odds | Fair implied probability | Offered odds (hypothetical) | Offered implied probability |
|---|---|---|---|---|
| Home | 2.00 | 50.0% | 1.90 | 52.6% |
| Away | 2.00 | 50.0% | 1.90 | 52.6% |
| Total across outcomes | not applicable | 100.0% | not applicable | 105.3% |
The 5.3% by which the offered implied probabilities exceed 100% is the margin embedded in those prices. You can run the same check on any market you see in an app: convert each displayed decimal price to an implied probability, add them, and subtract 100%. The result is the overround, a practical measure of how much margin the displayed prices contain. It describes one market at one moment, not an app’s overall margin.
Where the starting probabilities come from
For a single market, an operator may start from odds or probabilities generated in-house or supplied by a data provider, and then price the offer according to its own risk controls and commercial settings. Sportradar’s service page says it creates pre-match fixtures and base odds and offers tools to monitor and manage live offerings. The page reports scale figures of “~1M matches covered a year,” “70+ sports,” and “800+ sportsbook operators.” These are vendor-reported numbers, and the page snippet shows no publication year, so they should be read as Sportradar’s own description of its business rather than independently verified industry data.
Sportradar’s Alpha Odds product sheet lists the inputs its predictions combine. Those inputs include:
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- Ticket data
- Customer behavior
- Event ratings
- Pre-match and live data
These are vendor descriptions of one product. They are not an independently audited account of how any particular app uses them, and an operator may combine, weight, or ignore any of these signals differently.
Correlated selections in bet builders
Combined bets are where the independence question matters most. The table below uses hypothetical probabilities for two selections, each with a 50% fair chance, to show how the same two legs produce very different prices depending on the assumed relationship between them.
| Assumption | Joint probability (hypothetical) | Fair decimal odds |
|---|---|---|
| Independent (0.50 × 0.50) | 25% | 4.00 |
| Positively correlated (model estimate 40%) | 40% | 2.50 |
A bettor who multiplies the two leg prices, or who assumes the legs are independent when the model does not, is working from the wrong number. Neither figure here is drawn from a real market; they show why the correlation step changes the answer.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Live markets and data quality
Live prices can move as event information changes. Betfair’s Exchange API provides data retrieval and a low-latency stream that lets users subscribe to and track changes to market, price and order data. Betfair’s developer program describes that stream in this way:
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“The Exchange Stream API provides low latency access to market data allowing users to subscribe to and efficiently track changes to market, price and order data.”
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Betfair Developer Program, Guide to the Betfair Exchange API
Live pricing introduces operational problems that do not exist for a pre-match line. Betfair warns that third-party live data can be delayed or inaccurate, and it disclaims warranties about the accuracy, completeness and timeliness of that data. In-play markets are therefore sensitive to feed latency and display lag, not just to the underlying odds model.
Why a displayed price and an API price can differ
Betfair’s developer support explains that exchange prices can include virtual offers generated by cross-matching. Several everyday causes can make the price in an app differ from an API response or from the price you saw a moment earlier:
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- Data delay: the app is showing a feed that has not yet caught up with the latest market change.
- Settings: display or price-format settings can change what is shown without changing the underlying market.
- Virtualized offers: on an exchange, a displayed price may reflect matched or cross-matched offers rather than a single fixed quote.
- Repricing: on a fixed-odds book, the operator may reprice when event information or its own risk position changes.
Exchanges and matched prices
An exchange works differently from a fixed-odds sportsbook. Customers’ opposing positions are matched against each other, so the price on screen reflects bets that customers have placed or offered. Betfair says its Starting Price is produced by balancing backers, layers, and eligible Exchange bets at the event start. That is Betfair’s documented process, and it should not be taken as the design of every exchange.
| Feature | Fixed-odds sportsbook (Sportradar description) | Betfair Exchange (Betfair documentation) |
|---|---|---|
| Who sets the price | The operator, starting from base or fair odds | Customers’ backing and laying positions, matched against each other |
| Margin | Added on top of fair odds to produce offered odds | Not stated in the sources reviewed for this article |
| Correlated selections | Priced by a correlation step, for example in Bet Builder | Not stated in the sources reviewed for this article |
| Live data | Operator tools to monitor and manage live offerings | Low-latency stream of market, price and order changes |
| Starting Price | Not applicable to the sources reviewed | Produced by balancing backers, layers and eligible Exchange bets at the event start |
The comparison is limited to the documentation each source provides. Neither source shows a universal, cross-operator dataset, so the table describes how two named services are documented to work rather than how all apps compare.
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