What Is an Accumulator Bet? Accas Explained
By the MyHorseBets team · Updated · 15 min read
An accumulator is one bet that links several selections together, so the return from each winning leg becomes the stake on the next. Every selection has to win for the bet to pay. So the short answer to what is an accumulator is this: a single bet where the odds of all your selections are multiplied together, which makes the potential return big and the chance of collecting small.
Punters call it an acca for short, and you will see it on every bet slip, whether the legs are horses at the Cheltenham Festival or football teams on a Saturday afternoon. This guide explains how the maths works, what happens when a horse is a non-runner or dead heats, how acca insurance and boosts work, and why the bookmaker’s margin quietly grows with every leg you add. To check any of the numbers below, put them into our acca calculator.
What Is an Accumulator in Betting?
Wikipedia’s article on the parlay describes it as “a single bet that links together two or more individual wagers”, and notes that in Britain the same bet is called an accumulator or acca. In everyday UK usage the two and three selection versions have their own names, a double and a treble, and Wikipedia’s glossary of UK bets defines an accumulator as “a bet on four or more selections, all of which must win to gain a return.”
Acca Meaning and the Fold Names
Accas are named by the number of legs. Sky Bet’s bet types page describes a four-fold accumulator as “one bet made up of four selections in different events. If they all win, so do you.” A five-fold has five legs, a six-fold six, and so on. The word “fold” is simply the count of selections in the chain.
Doubles and Trebles Are the Smallest Accas
Sky Bet’s definitions are the same in spirit: a double needs both selections to win, and a treble needs all three. They work exactly like a bigger acca, just with fewer links. Our double bet calculator and treble calculator handle those two directly.
One Bet, Not Several
An acca is a single bet with a single stake. A £5 four-fold costs £5, not £20. That is the key difference from the full-cover bets further down this page, which split your stake across many bets.
How Does an Accumulator Work?
Each leg is settled in order. The stake and winnings from the first leg roll on as the stake for the second, then the third, and so on. In practice the bookmaker gets the same answer by multiplying the decimal odds of every leg together and multiplying the result by your stake.
Worked Example: a £5 Four-Fold
Four horses in four different races, at evens, 6/4, 5/6 and 2/1. In decimal odds (fractional plus one) that is 2.0, 2.5, 1.8333 and 3.0.
| Leg | Odds | Decimal | Running return |
|---|---|---|---|
| Start | £5.00 | ||
| Leg 1 | Evens | 2.0 | £10.00 |
| Leg 2 | 6/4 | 2.5 | £25.00 |
| Leg 3 | 5/6 | 1.8333 | £45.83 |
| Leg 4 | 2/1 | 3.0 | £137.50 |
The working: 2.0 x 2.5 = 5.0, then 5.0 x 1.8333 = 9.1667, then 9.1667 x 3.0 = 27.5. So the acca pays at 27.5 in decimal, or 53/2 as a fraction. £5 x 27.5 = £137.50 returned, which includes your £5 stake, so the profit is £132.50. If any one of the four loses, the return is £0. Our accumulator calculator runs the same sum for up to 12 legs. If you are not sure how to turn fractional odds into decimals, our odds calculator does it for you.
Why the Odds Multiply
Multiplying the odds is the same thing as rolling the winnings on. After leg one you have £10 riding on leg two; at 6/4 that £10 returns £25, and so on. That is also why a short-priced leg still matters: the 5/6 shot above almost doubles everything before it.
Fixed Price or SP in Each Leg
Each leg is settled at its own odds. If you take a price, that price is used; if you choose SP, the horse’s starting price is used. You can mix both on one slip. Our bet calculator settles an acca once you enter the prices from the results.
Disadvantages of Accumulators
The attraction of an acca is a big return for a small stake. The cost is less obvious. Two things work against you, and both get worse as you add legs.
One Losing Leg Loses Everything
The table below uses simple fair odds, with no bookmaker margin, purely as illustrative maths: these are not real statistics about horses or teams. At fair odds, the chance of a leg winning is one divided by the decimal odds, so an evens shot is 50% and a 2/1 shot is 33.3%. Our implied probability calculator converts any price this way.
| Legs | Chance all win, every leg at evens | Chance all win, every leg at 2/1 |
|---|---|---|
| 1 | 50% | 33.3% |
| 2 | 25% | 11.1% |
| 3 | 12.5% | 3.7% |
| 4 | 6.25% | 1.23% |
| 5 | 3.13% | 0.41% |
| 6 | 1.56% | 0.14% |
The chance of every leg winning is each leg’s chance multiplied together: 0.5 x 0.5 x 0.5 x 0.5 = 0.0625, or 6.25%, for four evens shots. Add a fifth and it halves again. Four 2/1 shots all winning is (1/3) to the power of four, which is 1/81, about 1.23%.
The Bookmaker’s Margin Compounds With Every Leg
Bookmakers don’t offer fair odds. The prices in a market add up, in implied probability, to more than 100%, and the excess is the overround. Wikipedia’s article on the mathematics of bookmaking explains that in a multiple bet “the effect of the overround in the book of each selection is compounded”, and gives the combined overround as the product of each book’s percentage, minus 100.
Take a simple two-way market priced at 1.9 each side (10/11). Each side implies 1 / 1.9 = 52.63%, so the book is 105.26% and the overround 5.26%. A fair price would be 2.0. Now chain four of those legs:
| Legs | Bookmaker acca odds (1.9 per leg) | Fair acca odds (2.0 per leg) | Return as share of fair |
|---|---|---|---|
| 1 | 1.90 | 2.00 | 95.0% |
| 2 | 3.61 | 4.00 | 90.3% |
| 3 | 6.859 | 8.00 | 85.7% |
| 4 | 13.032 | 16.00 | 81.5% |
A £10 four-fold at 1.9 per leg returns £130.32 if all four win, against £160 at fair odds. Using Wikipedia’s formula, the combined overround is 1.0526 x 1.0526 x 1.0526 x 1.0526 x 100, minus 100, which comes to about 22.8%. One leg gave the bookmaker a 5.26% edge; four legs give it more than four times that. A horse race has its own overround across the whole field, and the same compounding applies to every racing leg you add.
What That Means in Practice
None of this makes an acca a bad bet to enjoy for a small stake. It does mean the long-shot return is priced with a bigger built-in margin than the same horses backed singly, so it is worth knowing before you add the sixth or seventh leg.
Non-Runners, Void Legs, Rule 4 and Dead Heats
Racing throws up situations that football accas rarely see: horses withdrawn at the start, Rule 4 deductions and photo finishes that can’t be split.
A Non-Runner in Your Acca
Sky Bet’s bet settlement policy says that where a selection is void or does not run, “in accumulative bets the stake will run on to the remaining selection(s) with a Double becoming a Single, a Treble becoming a Double and so on.” In other words, the void leg is settled at odds of 1.0 and the bet becomes one fold shorter.
Using the same £5 four-fold, suppose the 5/6 horse is a non-runner. The acca becomes a treble: 2.0 x 2.5 x 1.0 x 3.0 = 15.0, so £5 returns £75 if the other three win. One important exception: Sky Bet’s non-runners page says that if your bet is ante post, a non-runner “will be classed as a losing bet”, so an ante post acca with a non-runner usually loses outright.
Rule 4 Inside a Leg
When a horse is withdrawn from one of your races and a Rule 4 deduction applies, the deduction comes off that leg’s winnings before the return rolls on. Sky Bet’s racing rules describe Rule 4 as deducting “a set value in pence out of every pound” of winnings. Say the 2/1 leg in our four-fold carries a 25p deduction. The £45.83 rolling into that leg would win £91.67 at 2/1, less 25% leaves £68.75, so the leg returns £45.83 + £68.75 = £114.58 instead of £137.50. Look up the deduction for any withdrawn price in our Rule 4 calculator, and check your bookmaker’s rules for exactly how it applies to multiples.
Dead Heats in a Leg
Sky Bet’s settlement policy says that in a dead heat “the stake money on a selection is divided by the number of runners involved in the dead heat.” In an acca, the stake on that leg is the running return. If the 6/4 horse in our example dead heats for first with one other, the £10 rolling onto it is split: £5 runs at 6/4 (returning £12.50) and £5 is lost. The final return is £12.50 x 1.8333 x 3.0 = £68.75, half the full £137.50. Our guide to dead heat rules covers the settlement in more detail.
Each Way Accumulators
An each way acca is two accas in one: a win acca and a place acca, each for the same stake, so £5 each way costs £10. Sky Bet’s racing rules say each way doubles and trebles “are settled win to win, place to place”, which means the win part only pays if every horse wins, and the place part pays if every horse at least places.
Worked Example: One Horse Only Places
Take the same four horses, £5 each way, and assume all four races pay 1/5 the odds for a place. Three horses win and the 2/1 horse finishes second. The win acca loses, because one leg didn’t win. The place acca pays, because a winner also counts as placed.
| Horse | Win odds | Place odds at 1/5 | Place decimal |
|---|---|---|---|
| 1 | Evens | 1/5 | 1.2 |
| 2 | 6/4 | 3/10 | 1.3 |
| 3 | 5/6 | 1/6 | 1.1667 |
| 4 | 2/1 | 2/5 | 1.4 |
The working: 1.2 x 1.3 = 1.56, then 1.56 x 1.1667 = 1.82, then 1.82 x 1.4 = 2.548. The place part returns £5 x 2.548 = £12.74. You staked £10 in total, so the bet returns £12.74 and the profit is £2.74. Place terms vary from race to race, so check each one. Our each way calculator applies one set of place terms to the whole bet, so it settles an each way acca exactly when every race pays the same terms; where they differ, multiply the place decimals by hand as above.
Why Each Way Accas Behave Differently
The place acca is made of short prices, so it returns little, but it is much more likely to pay than the win acca. It softens the all-or-nothing nature of the bet, at the cost of doubling the stake.
Acca Insurance and Acca Boosts
Bookmakers run promotions built around accas. These are offers, not bet types, and the terms change often, so the examples below describe what we read at the time of writing in October 2026. We don’t recommend any of them.
What Is Acca Insurance?
Acca insurance refunds your stake if exactly one leg of a qualifying acca loses. It does not pay out the acca: you get the stake back, not the winnings. If two or more legs lose, the bet loses as normal.
Typical Conditions
Paddy Power’s own guide to acca insurance, published on its news site in September 2023, listed conditions that were typical at that time: accumulators of “five selections or more”, minimum odds of 3/1 for the whole acca, horse racing and greyhounds excluded, and the refund paid “as a free bet”. That is the usual shape of these offers: a minimum number of legs, minimum odds per leg or for the whole bet, a cap on the refund, and a list of excluded sports and markets. When an offer says 5+ acca insurance, it means the acca needs at least five legs to qualify.
Refund as a Free Bet or as Cash
The form of the refund matters. A free bet has to be staked again under the bookmaker’s free bet terms before it can turn into money you can withdraw, while cash is yours straight away. Some racing products refund in cash instead: Sky Bet’s horse racing specials rules describe an “Acca/Place Insurance” bet where, “if exactly one selection in your insurance bet loses, your stake will be returned to your balance as cash.” The same rules say a non-runner means the bet is settled at reduced odds.
Acca Boosts and Enhanced Accas
An acca boost adds a percentage to your winnings, or a better price, if every leg wins. Sky Bet’s enhanced accumulators page describes special bets that “allow you to get better odds than if you were to manually add the same selections in to your bet.” A boost improves the payout but doesn’t change the chance of all legs winning, which is still the product of every leg’s chance.
Cash Out on Accas
Many bookmakers let you settle an acca early for a value they set. Sky Bet’s cash out page describes cash out as a feature “which allows you to settle an open bet for a value determined at the time of ‘cashing out’”, available on singles, multiples and accas. The same page notes cash out may not be offered if one selection in a multiple isn’t eligible, or while a market is suspended. The cash out figure is the bookmaker’s own valuation, so it also contains a margin. Sky Bet’s terms also warn that using cash out “may mean you will opt out of and no longer be eligible for a particular promotion (e.g. Acca Insurance)”, so read the offer terms first.
Accas Versus Full-Cover Bets
A straight acca needs every leg to win. Full-cover bets spread your stake over every double, treble and bigger combination of the same selections, so fewer winners can still give a return. Their definitions belong to their own pages; here is how they compare with an acca, using Sky Bet’s bet types page and Wikipedia’s glossary.
| Bet | Selections | Bets | Minimum winners for a return |
|---|---|---|---|
| Double | 2 | 1 | 2 |
| Treble | 3 | 1 | 3 |
| Four-fold acca | 4 | 1 | 4 |
| Trixie | 3 | 4 | 2 |
| Patent | 3 | 7 | 1 |
| Yankee | 4 | 11 | 2 |
| Lucky 15 | 4 | 15 | 1 |
Trixie and Patent
A Trixie covers three selections with three doubles and a treble, so a £1 Trixie costs £4. A Patent adds three singles for seven bets, so one winner gives a return.
Yankee and Lucky 15
A Yankee covers four selections with eleven bets and needs two winners. A Lucky 15 adds four singles, so one winner returns something. Note that a return is not the same as a profit: one short-priced winner in a Lucky 15 can return less than the total stake.
Choosing Between Them
The trade-off is simple. A £1 four-fold costs £1 and needs four winners. A £1 Lucky 15 on the same horses costs £15 and pays something with one winner. The acca keeps the stake small and the risk all-or-nothing.
Football Accas and Racing Accas
The word accumulator is used across every sport, and Google’s related searches show people asking what an accumulator is in football, in betting and in horse racing. The maths is identical in each: multiply the decimal odds, all legs must win. The differences are in the rules around the legs. Racing accas meet non-runners, Rule 4, dead heats, each way place terms and ante post rules. Football accas meet postponed matches and bookmaker-specific offers, which are often football only, as Paddy Power’s 2023 guide shows by excluding horse racing from its insurance.
Racing Accas at the Big Festivals
At meetings such as the Cheltenham Festival or the Grand National card, an acca across several of the day’s races is a common way to follow a whole afternoon with one stake. The same rules apply: every leg has to win, a non-runner shortens the bet by one fold, and each way terms apply leg by leg.
Keeping It in Proportion
An acca is a way to bet a small stake for a big potential return, and most accas lose. Set a budget you are happy to lose before you start, and treat any return as a bonus.
Betting always carries a risk of loss and no tipster, system or staking plan can guarantee a profit. Only stake what you can afford to lose, and set a budget before you start. Gambling responsibly.
Frequently asked questions
It is a bookmaker promotion on accumulators. If all your legs win except one, the bookmaker gives you back your stake, often as a free bet and up to a cap. You don't get the acca winnings, and if two or more legs lose there is no refund.
The offer only covers accumulators with at least five selections. A four-fold wouldn't qualify, even if just one leg lost. Most of these offers also set minimum odds, either for each leg or for the whole bet, so check both before you place it.
Your chance of collecting falls sharply with each leg, because all of them must win. The bookmaker's margin is also multiplied across the legs, so a four-fold pays noticeably less than fair odds would. One loser, even the shortest price on the slip, beats the whole bet.
It is a bet on several horses in different races, all of which must win. The odds are multiplied, so a few short-priced runners can build a large return. Racing accas also deal with non-runners, Rule 4 deductions, dead heats and each way place terms leg by leg.
In UK usage an accumulator usually means four or more selections, called a four-fold, five-fold and so on. Two selections is a double and three is a treble, though some sources call any chained bet of two or more an accumulator.