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ENFormula and example
Accumulator odds = the product of the odds of all selections1.80 x 1.90 x 2.00 = 6.84. A €10 stake returns €68.40 if all three selections win.
If one selection loses, the whole bet is lost. A void selection is usually settled at odds of 1.00, and the accumulator carries on without it.
Why the margin grows
Every selection carries a margin, and in an accumulator the margins multiply. For example, if each selection returns 95% of the stake to the player on average:
| Selections in the accumulator | Return to player | Kept by the bookmaker |
|---|---|---|
| 1, a single | 95% | 5% |
| 3 | 85.7% | 14.3% |
| 5 | 77.4% | 22.6% |
That is why hold on accumulators is higher than on singles. But the swings are bigger too: one winning long accumulator takes back what dozens of losing ones brought in.
Boost and insurance
- Acca boost: extra winnings for the number of selections, for example +10% for five or more. It is paid for out of the margin: on a five-fold at 1.90 per selection, where the fair price is 2.00, the bookmaker keeps about 15% of stakes even with the boost, against 5% on a single.
- Acca insurance: if exactly one selection loses, the stake is refunded, usually as a free bet. The cost of insurance is the probability of that outcome multiplied by the expected value of the free bet, not by its face value.
- Minimum odds per selection in the terms, for example 1.30 or higher. Otherwise players build the promo out of near-certain outcomes.
Common mistakes
- Correlated selections in one accumulator. A win for the favourite and the over in the same match often land together. Multiplying the odds then gives the player a price above the fair one, so such combinations are blocked or priced separately.
- Pricing the promo at face value. For the budget, count what was actually paid out: boost top-ups and winnings from insurance free bets.
- Judging accumulator hold on a single week. One big win pushes the week into the red, so look at a longer period.