Why accumulators are a gold mine for bookmakers
Published on 29 July 2026
The accumulator has everything going for it to appeal to recreational bettors: a few "safe" selections, odds that multiply, a spectacular potential payout for a small stake. What the interface does not show is that by multiplying the odds, you multiply something else too: the bookmakers' margins.
The mechanics
In an accumulator, the total odd is the product of the odds of each selection. But every odd carries its own margin. Multiply them, and the margins compound. The rule is simple and unforgiving:
RTP of the accumulator = RTP of selection 1 × RTP of selection 2 × …
Three selections taken on markets with a 95% RTP each: 0.95 × 0.95 × 0.95 = 85.7%. The margin has grown from 5% to 14.3%.
What it looks like as selections stack up
Assuming all selections are taken at a 95% RTP — a rather favourable level, typical of main markets:
| Selections | Accumulator RTP | Total margin |
|---|---|---|
| 1 | 95.0% | 5.0% |
| 2 | 90.3% | 9.7% |
| 3 | 85.7% | 14.3% |
| 4 | 81.5% | 18.5% |
| 5 | 77.4% | 22.6% |
| 6 | 73.5% | 26.5% |
| 7 | 69.8% | 30.2% |
| 8 | 66.3% | 33.7% |
At five selections, more than a fifth of the stake goes to margin; at eight, a third. And if the selections come from side markets priced worse than 95%, those numbers degrade even faster.
Why accumulators are pushed so hard
It is therefore no accident that betting interfaces make accumulators easy, suggest them and dress them up with dedicated promotions: they are, structurally, the highest-margin bets in the catalogue, and the ones that earn them the most. "Acca boosts" never offset the enormous compounded margin these bets carry by nature for the bookmakers (see the table above).
In conclusion
None of this makes accumulators forbidden: they offer a shot at a large payout for a small stake, and that asymmetry may be exactly what a bettor wants. But it has to be said plainly: over time, the accumulator is structurally the most unfavourable bet type for bettors. The RTP Calculator app was therefore not designed to compute the RTP of your accumulators. You can, however, measure the RTP of each of your single bets and, if you wish, see for yourself what multiplying the RTPs of your single bets would do to the overall RTP if you combined them.