The accumulator tax
An accumulator pays only when every leg wins. Under independent fair chances, each leg reduces the expected return again. Change the number of legs and the per-leg overround to see that cost.
Default margin: 6.53%, the market-average closing overround. The input is editable.
The market average is the overround of the averaged prices, which is lower than the margin of a typical single bookmaker.
Combined margin (expected stake loss): 46.87%; expected return per 100 staked: 53.13.
| Legs | Combined margin | Expected return per 100 |
|---|---|---|
| 1 | 6.13% | 93.87 |
| 2 | 11.88% | 88.12 |
| 3 | 17.28% | 82.72 |
| 4 | 22.35% | 77.65 |
| 5 | 27.11% | 72.89 |
| 6 | 31.58% | 68.42 |
| 7 | 35.77% | 64.23 |
| 8 | 39.70% | 60.30 |
| 9 | 43.40% | 56.60 |
| 10 | 46.87% | 53.13 |
| 11 | 50.12% | 49.88 |
| 12 | 53.18% | 46.82 |
| 13 | 56.05% | 43.95 |
| 14 | 58.74% | 41.26 |
| 15 | 61.27% | 38.73 |
Each leg multiplies the bookmaker's edge; a ten-fold at a 5% margin gives away about 39% of the stake in expectation.
Source: bookmaker_margins, market-average closing triplets; 62,016 priced matches, season start years 2021–2025, computed 2026-09-30 08:58:39 by football:index:bookmaker-margins (BookmakerMarginIndexer).
Five complete seasons per calendar: split-year editions are treated as complete after June 30, calendar-year editions after December 31; only recognised dated seasons and played matches. No opening-price fallback.
Method
For n independent legs with equal per-leg overround m (a fraction), expected return per unit = (1/(1+m))ⁿ. Combined margin here means 1 − (1/(1+m))ⁿ, the expected fraction of stake lost, rather than the accumulator overround (1+m)ⁿ − 1. Returns include the stake; negative margins imply a modelled gain.
What this does not claim: this does not model correlated legs, voids, boosts, taxes or limits; an average margin is not the exact margin on your selections.
Not betting advice