The uplift by number of legs
An acca boost raises the combined price of a slip by a step that grows with the number of legs. The step is real, and it is also the only boost that compounds the chance of losing, because every leg has to land for the uplifted combined price to pay.
- acca boosts sampled
- 288
- mean legs
- 3.4
- mean combined price
- 12.33
- mean boosted price
- 14.15
- mean uplift
- +14.8%
- uplift at 5+ legs
- +20.0%
An acca boost adds a step to the combined price that grows with the number of legs - about +5.0% at two legs and +20.0% at five or more in the sample. It raises the price of the whole slip, and it changes nothing about the chance of every leg landing.
The step grows with the slip; the chance does not
A single-selection boost moves one price. An acca boost moves the product of several, and the operator sizes the step by how many legs have to land. That is a rational response to a riskier customer bet, and it is why the boost looks generous exactly where the bet is hardest to win.
| Legs | Step | Offers | Share | Implied chance at 2.00 a leg |
|---|---|---|---|---|
| 2 | +5.0% | 72 | 25.0% | 25.0% |
| 3 | +10.0% | 96 | 33.3% | 12.5% |
| 4 | +15.0% | 84 | 29.2% | 6.3% |
| 5 or more | +20.0% | 36 | 12.5% | 3.1% or less |
Read the last column against the third. The uplift roughly doubles between two legs and five, while the implied chance falls by a factor of eight. The boost is larger and the bet is much harder.
What a step does to the price and to the chance
Worked example / sample F, three legs at 2.00, a +10.0% step
- the combined market price: 2.00 x 2.00 x 2.00 = 8.00
- the implied chance of all three landing: 1 / 8.00 = 12.5%
- the boosted combined price: 8.00 x 1.10 = 8.80
- the implied chance at the boosted price: 1 / 8.80 = 11.4%
- the uplift on a 10.00 stake if all three land: 10.00 x 0.80 = 8.00
- added expected value, at the market own chance: 10.00 x 0.80 x 0.125 = 1.00
Across the sample the mean slip was 3.4 legs and the mean combined price 12.33, against a mean boosted price of 14.15: an uplift of +14.8% on a bet whose implied chance was already in single digits.
What an acca boost is not
The growing step compensates for the added legs.
false The step is a percentage on the price; the added legs multiply the chance of losing. A +20.0% step on a five-leg slip does not restore the chance that two legs did not cost.
A bigger step means a bigger expected return.
partly true Measured per unit staked the added expected value rises with the step and falls with the chance. In the sample the effect was roughly flat across leg counts; nothing about the boost made the longer slip the better bet.
The acca boost and the single boost are the same offer.
false The single-selection boost is a price on one event. The acca boost is a price on a product of events, and the cap and revert rules that apply to it differ.