How accumulators work


It depends really, how much do you like money? If you hate it, they’re fantastic.

If, like me, you’re quite partial to a little spending cash, then – not so good.

Before we proceed, I should come clean and admit I’ve made the occasional accumulator bet myself. There’s a hidden value to these bets that’s sometimes ignored in gambling blogs – they’re quite fun!

I don’t see a problem with betting small amounts for the enjoyment of it all, if you’re happy in the knowledge you’re probably not going to win overall.

If, however, you’re striving to build a profitable betting strategy, it may be time to reassess whether accumulators, otherwise known as parlay or combo bets, should be involved in your game plan.

Understanding probability

When we have several events and we want to determine the probability of all of them occurring, we multiply the individual probabilities of each event to give us our answer.

Let’s use the classic example of a simple coin-toss to see how this works. We all know the odds to predict one flip is 0.5, or 50%, but what happens if we want to correctly predict a number of flips?

Coin Tosses Calculation Probability of success
2 0.5 x 0.5 0.25
3 0.5 x 0.5 x 0.5 0.125
4 0.5 x 0.5 x 0.5 x 0.5 0.0625
5 0.5 x 0.5 x 0.5 x 0.5 x 0.5 0.03125


As we can see, the chance of predicting the correct outcome halves with every turn. The chances of getting five in a row correct is just over 3%.

Assuming we had a big enough bankroll and could put enough volume in – the low chance of winning when predicting multiple events wouldn’t be much of an issue. The poor win rate would be balanced by the size of the pay-out when you did win.

The process of placing a bet with a bookmaker is a little more complex that predicting coin-flips, though, and that’s where the problem starts.


The chance to win big from a small stake, like we see in the example above, is appealing to us gamblers but how much are these long-shot bets costing us in equity?

Understanding the overround

In any event in life, the probability of all possible outcomes occurring adds up to 100%. When a bookmaker prices up a sporting event, however, the total of all the percentages will be a little higher. This is called the overround (also known as the juice, or vig) and is essentially the bookie’s profit margin.

Let’s take a closer look at a few Premier League matches, using the prices of a leading UK bookmaker;

Match 1 % X % 2 % Total
Tottenham Man City 3.75 26.66 3.60 27.77 1.90 52.63 107.06
Man Utd Sunderland 1.20 83.33 6.50 15.38 13.00 7.69 106.4
Newcastle Arsenal 5.25 19.04 4.00 25.00 1.61 62.11 106.15


From this table we can see this particular bookmaker is charging us at least 6% overround on each event. That figure is about standard for a high-street bookie but it is possible to find better deals out there.

Related: How arbing works

Pinnacle Sports is a good example, they offer an overround as low as 2% and if you don’t have an account yet we’d definitely recommend opening one for this reason (you can sign-up here).

Calculating the overround – how bookies make profit

So how do we figure out the total overround for an accumulator bet? We multiply the overround for each event in our selections.

For ease of calculation I’ll assume a standard overround of 6% for each of our picks;

Number of events  Calculation Total overround
2 1.06 x 1.06 (1.06^2) 1.12
3 1.06^3 1.19
4 1.06^4 1.26
5 1.06^5 1.33
6 1.06^6 1.41
7 1.06^7 1.50
8 1.06^8 1.59
9 1.06^9 1.68
10 1.06^10 1.79


The effect of multiplying the overround increases the bookie’s advantage with each event added, and this is why the bookies love us to place this kind of bet.

With just four selections we’re already giving away a 26% edge. With ten selections, you’re giving away a staggering 79%. That’s a bit like taking one number on the role of dice at even money.

So yeah, how much do you really like money?

Related: How to stop bookies limiting winning accounts
Related: Seven secrets bookies don’t want you to know
Related: How to become a professional gambler


About Author

Professional gambler & blogger. Say hello or shout abuse @tarrou22