Guides · last updated 2026-09-25

Accumulator bets: how the bookmaker's margin compounds, and what it costs you

An accumulator multiplies the odds of every leg. It also multiplies the bookmaker's margin. A 5% edge on one match becomes 28% on a five-fold and 63% on a ten-fold. Here is the arithmetic, a table for one to ten legs, and what it means for how you bet.

Written and maintained by Marek Ohanka, publisher, WhichBookmaker

Accumulators are the most popular bet in football and the most profitable product a bookmaker sells. Those two facts are connected. The appeal is obvious: small stake, big potential return. What is not obvious, because no bookmaker prints it, is that the margin you pay on a single bet is charged again on every leg you add, and the charges multiply rather than add.

What a margin is, in one paragraph

Every price a bookmaker quotes contains a fee. Convert a market’s odds into implied probabilities and they add up to more than 100%; the excess is the margin, or overround. On a typical Premier League match it is 4% to 7%. That is the bookmaker’s expected take on the bet, whatever you back. What a bookmaker’s margin is works through the calculation.

Why it compounds

Suppose a leg’s fair chance of winning is p. With a margin m, the bookmaker prices it as if the chance were p × (1 + m): a smaller payout for the same risk. On a single, you are underpaid by a factor of (1 + m).

Put five legs together and each leg carries its own (1 + m). The combined odds are the product of the five prices, so the underpayment is (1 + m)⁵. At m = 5%:

(1.05)⁵ = 1.276, so the combined margin is 27.6%, not 25%.

Turn that round and it says what share of a fair return you actually get: 1 ÷ 1.276 = 78%. The bookmaker keeps the other 22% of the fair value of the bet before a ball is kicked.

The table that should be on every acca slip

Combined margin and the share of a fair return you keep, at 3%, 5% and 7% per leg.

Legs 3% per leg 5% per leg 7% per leg
1 3.0% (97%) 5.0% (95%) 7.0% (93%)
2 6.1% (94%) 10.3% (91%) 14.5% (87%)
3 9.3% (92%) 15.8% (86%) 22.5% (82%)
4 12.6% (89%) 21.6% (82%) 31.1% (76%)
5 15.9% (86%) 27.6% (78%) 40.3% (71%)
6 19.4% (84%) 34.0% (75%) 50.1% (67%)
8 26.7% (79%) 47.7% (68%) 71.8% (58%)
10 34.4% (74%) 62.9% (61%) 96.7% (51%)

The percentage is the combined margin; the figure in brackets is the share of a fair payout you receive. A ten-fold at a 7% bookmaker pays roughly half of what a fair price would.

Run your own legs and margin through the accumulator calculator, which does this arithmetic for any number of selections.

A worked example

Five Premier League favourites, each at 1.50 with a 5% margin. Combined odds 1.5⁵ = 7.59, so £10 returns £75.94 if all five win.

At fair prices each leg would be about 1.575 (1.5 × 1.05), and the combined odds 9.69: a return of £96.90. The gap between £96.90 and £75.94 is £20.96, or 21.6% of the fair return. On a bet that most people think of as “five short-priced favourites, nearly a sure thing”, the bookmaker has taken a fifth of the value before the weekend starts. The five-fold will also lose more often than intuition suggests: even at a true 63% each, five of them together win 10% of the time.

What follows for how you bet

Fewer legs. Each leg you add multiplies your potential return and the bookmaker’s margin by the same mechanism. Two or three legs keep most of the value; eight to ten give most of it away.

Margin matters more than on singles. A bookmaker with 3% margins versus one with 6% is a small difference on a single and a large one on an accumulator: 16% versus 34% on a five-fold. This is why our best odds ranking scores operators on margin and why the gap between them is worth more to acca bettors than to anyone else.

Boosts and insurance are priced by people who know this table. An “acca boost” of 10% on a five-fold at 5% margins still leaves you 20% short of fair. Acca insurance, which refunds the stake as a free bet if one leg loses, usually requires five or more legs at minimum odds: the extra margin of the qualifying legs is normally worth more than the refund. Neither is a reason to add legs you would not otherwise have picked.

Short-priced legs are not free. A 1.10 selection adds 10% to your return and a full margin to the bet. If it is there to “make the acca bigger”, it is making it worse.

Non-runners and voids help slightly. A voided leg is settled at 1.0 and removed, which also removes its margin. The bet shrinks to the remaining legs at their own prices.

The honest summary

An accumulator is not a scam; it is a product with a high price that is never printed. The price is (1 + margin)ⁿ − 1, and it rises faster than the odds do. Keep the legs few, choose the bookmaker with the lowest margin, and treat boosts as marketing for a product that already makes the bookmaker more money than any other.