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Decimal odds

What Is A Bookmaker?

Under normal circumstances the bookmaker is the only part in a bet that definitely comes out as a winner.

In order for the bookmakers to keep doing business they need to make bets that allow them to make money each time they offer a bet. Therefore, bookmakers don’t set the odds just based on probabilities. They also incorporate a margin ensuring they earn a profit on each bet.

A Coin Toss Example

Let’s take a basic coin toss for £100 as an example:

The outcome is either heads or tails, so it is a 50/50 chance. One person bets on heads and another on tails. No matter who wins, the bookmaker would have to pay out the £100, leaving no surplus for him.

That would be a rather bad business plan.

Let’s now say that the bookmaker lowers the payout to £90, instead of the fair £100. This is the equivalent of offering 1.90 odds instead of the fair 2.00. Since our two punters still wager the £100, the bookie will turn a profit whatever the outcome is, since he collects £100 from one punter and pays out £90 of those to the other punter, keeping £10 for himself.

This represents the bookie margin, also known as the commission, the “Vig” or “juice”, mostly in the US. And it is what makes betting such a challenge as you not only have to pick winners, but also do so at a rate of return that is greater than the bookmaker margin.

Beating the Margin

In other words, picking 5 winners out of 10 with each paying fair odds of 2.00 without any bookmaker commission would see you break even. However, receiving standard bookmaker odds of 1.90 with the 0.10 commission off of the fair odds of 2.00, picking 5 winners would see you make a loss of 5% on your total investment. 

How so?

We outlay 10 units, picking 5 winners at 2.00.
5 winners x 2.00 = A return of 10.
We break even on our outlay of 10 units.
But with standard bookmaker commission on odds of 2.00 at 5%, we receive a return of 1.90.
5 winners x 1.90 = A return of 9.5.
We make a loss of 0.5. Or in other words, 5% of our outlay of 10 units.

As you can see, when people refer to “beating the bookmaker”, what they are really saying is that success in betting long term, means beating the bookmaker margin.

It goes by many names: the Juice, the Vig, the Margin, the Commission, The Take, The Percentage, The Cut. Whatever you want to call it, it’s that slice of action every bookmaker takes out of the odds so as to make their business worth their while.

And it varies from bookmaker to bookmaker and even from event to event with bookmakers sometimes offering special ‘reduced juice’ on particular leagues or tournaments to attract customers, offering bettors higher odds and greater returns than those on offer at competing bookmakers.

But what exactly are bookmaker betting margins? How do you calculate them? How much commission are you paying with each bet and what impact can it have on your betting returns?

What Are Bookmaker Margins?

Some believe that bookmakers are ‘risk takers’, that the odds offered by bookmakers are more a reflection of who the bookmaker thinks will win a particular contest and that in affect, bookmakers have a preferred winner in any given contest. This is only half true.

Yes, bookmakers may have a preferred winner in any given contest, but it’s not in any way a result of favouring one side when framing the odds. And a risk taker is exactly what a bookmaker is not.

When framing odds for a particular event, bookmakers are attempting to set odds that they think will attract betting on both sides of the market, therefore balancing the bookmaker’s liability given the possible outcomes.

But if the bookmaker’s liability is equal given any outcome, how does a bookmaker make a profit themselves? The answer is of course, the margin.

Bookmakers take this slice out of the odds they offer, resulting in a profit, or ‘margin’ once their liability is balanced on either side of the odds. In other words, the margin is the percentage of money taken from bettors that the bookmaker will claim should they balance their liability perfectly. And although it’s unlikely that a bookmaker will achieve that perfectly balanced liability on each side of a specific event, by offering hundreds of markets each day on a wide range of sporting events, they can be confident that their overall liability will even out and they can take their cut of the money put down by bettors.

What Is A Fair Market?

So what’s an example of a market with the bookmaker margin taken out? Well, the clearest example to offer is on so-called ‘even money’ events. This is where it is deemed by the bookmaker that both sides of the market will attract equal action from a betting public that considers each outcome as an even probability, 50-50.

So let’s use the example of tossing a coin. We can expect that over enough tosses, it is 50% as likely that a coin will come up heads as it will tails. Now if bookmakers were offering a fair market without a margin, the odds would of course be an even 2.00 on both heads and tails. i.e. you bet 1.00 to win 1.00. This is what is known as a ‘100% market’ or ‘fair odds’. In other words, you’re getting full value on your return.

But bookmakers want their slice of the action. They’re in business to make money after all. To do so they offer us odds of anywhere between 1.85 to 1.99 as ‘even money.’ They take out their percentage. They do not offer full price. This is the business.

So for example, if we were being given fair odds of 2.00 for a coin toss, essentially a 50-50 event, over a sample size of thousands of £1 bets, it is likely that we will not lose any money. Half the time we will win, giving us a profit of £1, half the time we will lose, giving us a loss of £1. But a bookmaker will not offer us these odds. They want to make money so they are more than likely to offer us odds in the range of 1.90 for a coin toss. This then means that for every £1 that we bet, we will on average only see £0.90 returned, averaging a loss of £0.10, which of course, the bookmaker claims. This is how they make their money, by not offering fair odds on a given outcome.

Calculating Betting Market Margins

As we said, a 100% Market is where ‘fair odds’ are being offered. It is where there is no advantage for either the bettor or the bookmaker. When the market is assessed as less than 100%, this places the advantage with the bettor, meaning there is greater value in the odds than the probability of all possible outcomes. On the other hand, when the market is greater than 100%, as it typically is, this means there is less than full value in the market. The advantage is with the bookmaker.

So how do we calculate the margin for a given betting market?

Well, it’s a fairly simple calculation. Firstly, we need to convert the decimal odds to the percentage probabilities that they represent, what is known as their ‘implied probability’.

So let’s take an example, the odds of 1.65. We convert these odds simply as 1 divided by 1.65 which equals 0.606. We do this for each possible outcome in the event, add them together, then multiply that by 100 and we get the market percentage also known as the ‘overround’.

Here’s an example. Let’s take a football game, with 3 outcomes – either team wins or there is a draw.

  • Team 1 odds: 2.00
  • Team 2 odds: 3.90
  • Draw odds: 3.50

We make our conversions and we get –

  • Team 1 probability: 1 divided by 2.00 = 0.500
  • Team 2 probability: 1 divided by 3.90 = 0.256
  • Draw probability: 1 divided by 3.50 = 0.286
  • Total = 1.042
  • Market Margin = 104.2%

Now to calculate the average commission you pay on each bet, given the margin. There are a number of ways to calculate the commission on specific odds. Our preferred way is the following:

So let’s take our example of the football game further to calculate the margin:

  • Commission = (1 – (1 / Market Margin)) * 100%
  • Commission = (1 – (1 / 1.042) * 100%
  • Commission = (1 – 0.96) * 100%
  • Commission = 4%

So in this example, for every £100 that you bet, you are paying an average of £4 to the bookmaker. Or in other words, at a commission rate of 4%, you would be offered odds of 1.92 on a coin toss.

Of course, you’re not going to want to have to do this each and every time you wish to make a bet, especially if you’re trying to calculate the value in a horse racing market of 12 or so runners. Fortunately, betting exchanges such as Betfair display the Market Margin on each market. There are also a number of calculators on the web that will do it for you.

Bookmaker Commission Excel Calculator

The bettingexpert Market Commission Calculator will tell you just how much commission you’re paying on any particualr market. Are you getting a fair price or are you paying too much to bet with your bookmaker?

Here’s how the calculator works:

Step 1 – Choose your preferred odds format. The bettingexpert Market Commission Calculator can assess the amount of commission for a particular betting market in three popular odds formats – decimal, American and fractional.

Step 2 – Enter the odds offered by your bookmaker for each possible outcome in a given event.

Bookmaker commission calculator

Step 3 – Once you’ve entered your bookmaker’s odds, the Market cell will display the total value in the market, while the Commission cell will tell you exactly how much you’re paying in commission on that market. Unless you really have a sharp angle on a market, we wouldn’t recommend betting on market with a commission greater than 5%.

Bookmaker commission calculator

How Do Bookmaker Margins Impact Your Returns?

We hopefully now have an understanding of what bookmaker commission is. Let’s then have a look at the value of shopping around for the best value markets. We’ll do this via a simple comparison of various ‘even money’ odds and see the impact a slight reduction or increase in commission can have on your betting bank. Here we bet 1,000 bets at varying ‘even money’ coin toss odds based on market margins.

Market Margin Commission Coin Toss Odds 55% Win Rate Return 53% Win Rate Return
100.5% 0.5% 1.99 9.45% 5.47%
101% 1% 1.98 8.90% 4.94%
101.5% 1.5% 1.97 8.35% 4.41%
102% 2% 1.96 7.80% 3.88%
102.6% 2.5% 1.95 7.25% 3.35%
103.1% 3% 1.94 6.70% 2.82%
103.6% 3.5% 1.93 6.15% 2.29%
104.2% 4% 1.92 5.60% 1.76%
104.7% 4.5% 1.91 5.05% 1.23%
105.3% 5% 1.90 4.50% 0.70%

We can see here that the difference between betting on a market with a commission of 2.5% and 5% results in 2.75% greater return with a winning strike rate of 55%. And when we are talking slight percentages between being a successful bettor and a losing bettor, assessing the margin in the markets you choose to bet on is so very crucial.

And that’s winning at a 55% rate on ‘even money’ coin toss odds. Let’s consider what impact a reduction of margin can have on a 53% winning strike rate. You can see here that the impact is significant. With a commission of just 2.5%, a 53% strike rate on 1,000 ‘even money’ coin toss bets will gather a return of 3.35%. But with a commission of 5%, the return is just 0.7%.

Take Best Odds Available Always

While the conclusion is obvious, that it is far more beneficial to bet with bookmakers who offer better value markets, it’s something that many novice bettors don’t quite understand. And now with online betting, the ability to play one bookmaker’s odds off against another, the opportunity to reduce our commission is greater than ever, particularly with the advent of betting exchanges.

Let’s consider this example. We have a range of odds on offer from a 5 different bookmakers for an upcoming Premier League match between Manchester United and Arsenal.

Result Betway BetVictor Unibet Skybet Pinnacle
Man Utd Win 2.50 2.60 2.55 2.44 2.55
Draw 3.20 3.20 3.25 3.30 3.25
Arsenal Win 3.00 3.00 2.80 3.00 3.10
Market 104.58% 103.04% 105.70% 105.30% 102.24%
Commission 4.38% 2.95% 5.39% 5.04% 2.19%

We can see that from bookmaker to bookmaker, Pinnacle Sports is offering the best odds with a commission of just 2.19%. That’s a very low commission rate. But we can improve it even more by only taking into account the best odds available for each outcome, highlighted above in red. By considering only best odds available, our overall commission rate improves from a 2.19% betting only with Pinnacle Sports, to 1.01% when taking into account the best odds available across every bookmaker.

Result Bookmaker Odds Implied Probability
Man Utd Win BetVictor 2.60 38.46%
Draw Skybet 3.30 30.30%
Arsenal Win Pinnacle 3.10 32.26%
 Market 101.02%
 Commission 1.01%

Again, the point should be clear. It’s incredibly important to take the best odds available in order to reduce your commission rates as much as possible. So make sure you have a portfolio of bookmakers that allows you to take the best odds available more often than not.

It may seem like a slight percentage, and it may seem that odds of 1.90 are only slightly less than odds of 1.95, but over the long run it makes a huge difference to your overall chances of success as a sports bettor. 


Betting without a bookie

For a truer indicator of how much a bet is worth you might turn your attention to the section about betting on exchanges such as Betfair and Betdaq.On a betting exchange users bet against users, and the market is driven by supply and demand only, often resulting in better odds compared to those of the bookmakers. However, it is very important to take into consideration that exchanges charge 2-5% commission on winning bets, thus prices may look more attractive as they actually are when accounting for commission. The commission itself is actually not that different from the bookmaker’s margin as a concept, but most bookmakers build in a bigger margin than 5%, so you’re mostly still better off with a betting exchange.