How do Betting Odds Work?

Let’s say the Masters is around the corner, and you are certain that Rory McIlroy will be donning that famous green jacket. So sure, in fact, that you want to put a bet on it. So you make your way down to your local bookmaker, cash in hand, but on arrival you are confronted with a wall of numbers and figures.

Those numbers and figures are odds, and they are applied to every event in sport. Odds are pivotal to the world of betting, but what exactly are they and how do they work?

What are betting odds?

Odds are figures applied to betting which denote the winnings a bet will receive based on the amount staked. Odds are not set in stone, and they can shorten or drift. If they shorten, the potential winnings shrink. Drifting means the potential winnings increase.

Evens means that the winnings are identical to the stake, so if you bet £5, you win £5 – as well as getting your stake back. So evens means you double your money.

If the betting odds are bigger than evens the winnings exceed the stake, so a winning 10/1 bet means you pick up £10 if you bet £1, plus your stake.

If odds are shorter, that is to say, lower than evens, your winnings will be smaller than your stake. So betting on something that is 1/10 means if you bet £1, you’ll receive just 10p profit if it pays off – £1.10 back in total.

Probability in betting

Bookmakers decide odds on events based on carefully established probabilities. A lot of research goes into each match, meeting or tournament so accurate odds can be formed.

If Justin Rose is at 10/1 to win the US Open, this will be down to a number of factors. He has won the US Open before, for instance. He may prefer the type of course that hosts the competition, or could be in a good run of form.

If his odds drift to 18/1, it could be because he is recovering from an injury or has missed the cut in the last couple of tournaments. It is useful to do your research when placing a bet, because it explains why odds are what they are.

Types of Odds

Fractional odds

Fractional odds are the most commonly used form of odds in British betting. The number on the left of the odds represents the winnings, while the one on the right represents the stake. For instance, if McIlroy turns out to be 6/1 favourite to win the Open, a £1 bet wins you £6, plus your original stake, so you would take £7 home.

Decimal and American odds

Decimal odds are used in Europe, and are also worth knowing because they are also the main odds format at betting exchanges such as Betfair. The stake is actually factored in to decimal odds, so making a £10 stake with odds of 2.5 mean your winnings, stake included, are £25. That’s equivalent to making a bet with 6/4 fractional odds.

American odds are based on a system of positive and negative numbers. A positive number shows the profit you would make if you bet £100. Therefore betting £100 on a team with odds of +150 wins you £150, plus your £100 stake is returned. Negative numbers indicate the amount you would need to bet to make £100. So if a team is -200, you would have to bet £200 to make a profit of £100.

Odds comparison

A price of 10/1 is easy enough to work out, but what if you have £5 in your hand and want to know whether 5/7 or 7/11 provides better odds? The main issue with fractional odds are that they do require some maths, and it totting up your card on a Saturday afternoon is as good as your maths gets, that could be an issue! You would have to make the denominators equal, so 5/7 becomes 55/77 and 7/11 becomes 49/77. Therefore, we can see that 5/7 is slightly better. It is much easier with decimal odds – it would be 1.71 and 1.64, so it is much clearer which offering is the bigger of the two odds and which provides better winnings. Decimal odds are much friendlier to novice punters, so if possible ask for decimal odds rather than fractional.

Converting Fractional to Decimal – One easy way to compare fractional odds is to convert them into decimal and this is a simple enough task. The top number of a fraction, that is to say the number on the left (so 10 in odds of 10/1) is the numerator whilst the number on the bottom/right (1 in the case of 10/1) is the denominator.

Just divide the numerator (left) by the denominator (right) and add 1 (the one represents the stake, which is shown as the returns in decimal odds but not fractional). So 10/1 is 10 divided by 1, plus 1 = 11. 6/4 is 6 divided by 4 plus 1, so 2.5, whilst 8/11 is 0.727 + 1, with bookies usually giving fractional odds of 1.73.

Of course, if you are using our betting tips then you won’t need to compare odds because we’ll always highlight the best available odds from the various leading betting sites we feature.


Accumulators look a lot more complicated than they are. Let’s keep this as simple as possible, and assume you have put on a two-fold accumulator, usually known as a double. You have staked £5 on Rory McIlroy to win at 6/1 and Bubba Watson to place top five at 2/5 in an alternative event.

Your stake is placed on your selection for the first bet. If it wins, then the winnings are placed on the next selection, and so on. So McIlroy wins at 6/1 and you have a grand total of £30, plus your £5 stake. That £35 is then placed on Bubba Watson, which means you end up with £49. Simple, right?


Odds can at first seem difficult to work round, but the basics are quite simple. For fractional odds, the bigger the number on the left is than the number of the right, the longer the odds are, the more you win but, of course, the lower the chances – in theory at least – of your selection winning.

For decimal odds, the larger the number, the larger the winnings and decimal odds simply reflect the amount of money you will get back based on a £1 stake. Comparing odds takes some quick maths for fractional odds, but for decimal odds it is much simpler.

However, if those calculations make you that extra profit, it is well worth the time.So, if you get the urge to make a bet, take a good look at the odds before you make a decision. Odds can differ between various bookies by as much as 20% – sometimes even more. That can make a big difference to your winnings, especially in golf where long odds winners are far from uncommon (John Daly in the 1991 USPGA anyone?!).

Given all the different bookies offer new customers free bets or enhanced odds (or sometimes even both!) when they first join, it makes sense to join a few different betting sites, because not only will you grab a nice freebie, you’ll also give yourself a wider range of odds to choose from.