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Illustrative calculations only. Prices and probabilities entered here are not verified event forecasts or offers.
How combined accumulator odds are calculated
In a standard multiple that pays according to decimal leg prices, the combined decimal price is the product of all leg prices. For three hypothetical selections priced 1.80, 2.00 and 1.65, the combined price is 5.94. An illustrative stake of 10 units yields 59.40 units gross return and 49.40 units net profit if every qualifying selection wins.
This arithmetic applies to normal multiplication of leg prices and does not automatically apply to correlated same-event selections, boosts, promotional enhancements, each-way bets, system bets or unusual settlement rules. A bookmaker’s accepted bet slip is the final record of the actual offered price and market conditions.
Implied probability from combined price
The reciprocal of combined decimal price expresses its break-even implied probability. A quote of 5.94 corresponds to about 16.84 percent. This number is a consequence of the quoted price; it should never be described as a verified forecast of the event sequence.
If true probabilities were independently estimated for different events and those events were statistically independent, their joint probability would be the product of those estimates. Sports outcomes within the same contest are often dependent, so multiplying probabilities without a documented independence assumption can be materially wrong.
Entering legs and handling invalid values
The tool accepts from two to eight leg prices and a positive stake. An add-leg control appends an input, while a remove-leg control allows a user to delete a row down to two selections. Inputs must be finite decimal numbers greater than one; blank fields and negative values produce a visible validation message.
All displayed results derive from current entered values. The calculator does not impose an arbitrary favourite, invent an event, fetch real-time odds or silently replace invalid entries with default values. It recalculates only a potential contractual payout and a pricing-based probability under a simplified model.
What happens when a leg is void
Rules governing void selections differ between operators and products. A typical ordinary multiple may be recalculated using only valid remaining selections, but ante-post bets, enhanced multiples and certain promotional wagers can have different procedures. The calculator assumes every included leg is valid and active.
Do not simply enter a zero price or treat a void as a losing selection without checking the operator’s written settlement terms. If the appropriate rule removes the leg at odds of one, a user can delete that leg and recompute the remaining hypothetical multiple, provided at least two selections remain. A single remaining selection may settle as a single bet, which lies outside this multi-leg interface.
Correlated outcomes, costs and prudent interpretation
BuildABet and other same-event combination products can price correlated outcomes differently from an ordinary accumulator. Multiplying separate singles may produce a price that the bookmaker never offers. An educational calculator cannot reproduce proprietary same-event pricing.
Even a high advertised gross return does not imply that the corresponding wager is sensible or likely to win. No probability, selection strategy, number of legs or stake-sizing system guarantees profit. The available bankroll should never be treated as disposable unless its complete loss would be acceptable.
A comparison of two-leg and three-leg combinations
Using the default prices 1.80, 2.00 and 1.65, the three-leg combined decimal price is 5.94. Removing the third valid leg produces a two-leg price of 3.60, with a 10-unit stake giving a potential gross return of 36 units. The larger three-leg payout is conditional on one additional result and does not mean that the third selection increased the mathematical attractiveness of the first two.
Suppose each leg were instead offered at decimal 2.00. Two legs would give 4.00, three would give 8.00, and four would give 16.00 before special product terms. These multiplied figures show how headline returns grow while the full combination demands more successful conditions. Price-implied probabilities would correspondingly be 25 percent, 12.5 percent and 6.25 percent, none of which independently verifies a true forecast.
Why eight selections is a display limit, not an edge
This implementation caps the number of entered selections at eight to keep the form accessible on small screens, not because eight represents an optimal betting strategy. As more prices are multiplied, the potential quoted gross payout rises, but the number of independent conditions that must all succeed also rises. Promotional incentives and special accumulator insurance can change contractual returns and must be assessed against the operator’s own rules, not assumed to be included in the simple calculator.
Sources and further reading
The worked calculations are original illustrations. Official operator rules and regulatory information help distinguish mathematical outcomes from actual product terms.
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