Peter has been writing for the gambling industry since 2013, and joined the SportsCasting team in July 2024. Outside of work Peter is a runner, gig rower, guitarist and musician (releasing two albums under the name 'ShiroToKuro'). Peter is also a lover of manga, anime and Japanese cinema and can even read and speak Japanese at the conversational level.
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Ian Bruce became interested in betting in 1987, when he landed a winning Yankee on his first attempt. That stroke of luck (and he admits that's exactly what it was) sparked an interest in understanding the strategies behind successful wagers. Over the years, he has become one of the UK's most prolific writers on betting and gaming, and is best known for his systematic approach to winning. Ian's career in the industry now spans over three decades. His favorite betting method is Dutching because, in his words, "It's the one I win with more often than not."
All posts by Ian BruceA full explanation of betting odds – what they represent, how they are worked out and how you use them to calculate potential winnings and value from your bets.
What Are Betting Odds?
Betting odds are the most common representation at bookmakers of the probability of an outcome coming true. They also represent the amount of money you get back from a bet should you choose to place it and it’s successful.
The classic way of presenting betting odds at UK bookmakers is with fractional odds. If, for example, a competitor is at odds of 5/2, then it is thought that if the event they are competing in took place seven times (5 + 2), they would win twice and lose five times. Expressed as a percentage, this would give them a (2/(5+2)) = 28.6% chance of winning.
If you were to back the competitor with £10 and they won, your bet would win £25, as (10*5)/2 = 25. You would also get back your winning stake for a total return of £35.
How to Read Betting Odds
There are three main types of betting odds displayed at UK online bookmakers. Fractional odds, as you have just seen, are expressed as a fraction and are the traditional way of representing odds. Decimal odds are represented by decimal numbers, which is a more modern way of representing odds. American odds are less popular in the UK. They represent winnings from a $100 bet or what you need to bet to win $100, depending on the value of the fixed odds.
How to Read Betting Odds – Same Odds, Different Representations Fractional Decimal American 5/4 2.25 +125 Let’s now take a closer look at the different types of odds in turn:
Fractional Odds
Fractional odds have been used for centuries in the UK. They are easy to understand: To gauge the chances represented by them, you just add the two numbers together with the number after the ‘/’ or ‘-‘ representing a successful outcome. So, 4/6 is six chances out of ten, 15/8 is eight chances out of 23, and so on.
You simply do the maths to calculate winnings from a bet using fractional odds. A £5 winning bet at odds of 15/8 wins £9.38. With fractional bookmaker odds, your returns are not included, so you need to add your stake to see what you’re getting back from the bookie.
Decimal Odds
This odds format is a relatively modern way of representing odds and is particularly popular with more youthful bettors. They are used to represent the full returns from a bet as opposed to just winnings. However, the chances of a bet winning are more difficult to work out. The best way to approach this is to remember that 2.00 represents a 50/50 chance, such as the toss of a coin. Decimal odds under 2.00 are ‘odds on’. Such betting odds suggest that it is more likely for an outcome to occur than for it not to.
Decimal odds calculate returns, not winnings, so it is important to remember that. Again, working our returns is just a case of doing some simple arithmetic – a £5 bet on odds of 2.88 will return £14.38, as 5 multiplied by 2.88 is 14.38.
American Odds
American odds can be positive or negative. Negative odds represent the favourite, and positive odds the underdog. The number is in relation to a $100 bet. If the odds are positive, they represent winnings from a $100 bet. If the odds are negative, they represent what you need to bet in order to win $100. American odds calculate winnings, not returns.
If you place a £5 bet at odds of +187.5 then it’s just maths (again) as 5 x 187.5 = 937.5, then divide by 100 (as the odds represent a $100 bet) to get £9.38 as your winnings. With negative odds, you divide, so with odds of -275 and a £5 bet it would be 5 / 275 = 0.0182 and then multiply by 100 to get £1.82.
Why Betting Odds Are Important
All bets are about risk. When you place a bet, the bookie is saying, ‘Give me money, and if your bet wins, I’ll give it back to you with something extra on top’. The odds represent the amount of ‘something extra’ you will get back, so it’s important you understand ‘what are the odds?’
Odds also represent the chances of a competitor winning. In a horse race, a mount priced at 2/1 is thought to have a much better chance of winning than a mount priced at 5/1, and so on. Understanding odds and the probabilities they represent is key to being a successful placer of bets. It might also help bettors to avoid overestimating their chances, as discussed in this article in American Scientist.
Fixed odds can be a good measure of a bookmaker. If you are betting on Sabrimento to win the 4.15 at Newbury and one bookie is offering odds of 5/1 and a different bookie has odds of 4/1, then you’d go with the bookmaker offering the more beneficial odds.
How to Convert Fractional Odds to Decimal (and Vice Versa)
Fractional odds and decimal odds are the most common ways of representing odds at UK bookmakers, and most bookies will allow you to switch between the two if you prefer one to the other. It is, however, important that you know how to convert fractional odds to decimal odds and vice versa.
It’s a question of maths again, and to convert from fractional to decimal, you consider the gambling odds as a sum and add one. So, odds of 5/2 become five divided by two, which is 2.5, and then adding one to successfully convert to 3.5 (or 3.50, as some bookies will always display decimals odds to two decimal places like monetary prices).
Converting back is a three-step process. First, you subtract one, then you put the result above 1, and then you simply make a proper fraction. So, 3.5 minus 1 is 2.5, which becomes 2.5/1 or 5/2. For ‘odds on’ prices, it’s the same – 1.80 becomes 0.8/1 or 4/5.
How to Calculate Potential Winnings
There are four rules to calculating potential winnings depending on how you like your odds, and we take a gander at them all below.
Fractional OddsDecimal OddsPositive American OddsNegative American OddsFractional Odds
Multiply your stake by the price to calculate your winnings. Add on your stake to get your returns.
Decimal Odds
Multiply your stake by the price to calculate your returns. Subtract your stake to get your winnings.
Positive American Odds
Multiply your stake by the price, then divide by 100 to get your winnings. Add on your stake to get your returns.
Negative American Odds
Divide your stake by the price, then multiply by 100 to get your winnings. Add on your stake to get your returns.
How Betting Odds Are Determined
Online bookmakers use specialist providers and technical systems to work out the odds they offer. They begin with the implied probability of a specific outcome becoming the result of an event. They then add a little bit on top as ‘the juice’ to make sure that they remain profitable. The probability is then converted into sports betting odds.
Nearly all odds determination is now done by computers, and odds for all events are constantly monitored. External factors contribute to odds determination, too. For example, if large sums are placed on a specific competitor, then the sports betting odds of that competitor will tighten to minimise potential bookie losses.
You can work out the implied probability (the chances of an outcome) from the odds that are published on betting sites. To do so, it’s easiest to use fractional odds, so you may need to convert. If the odds are represented as x/y then probability is simply y/(x+y). So, sports betting odds of 9/5 have an implied probability of 35.7 per cent as 5 divided by 14 (9 + 5) is 0.3571 (multiplied by 100 to get the percentage).
We’ve outlined some common odds and implied probabilities in the table below.
Fractional Decimal American Implied Probability 2/7 1.29 -350 77.8% 4/11 1.36 -275 73.3% 1/2 1.50 -200 66.7% 4/5 1.80 -125 55.6% 5/6 1.83 -120 54.5% Evens (1/1) 2.00 +100 50.0% 5/4 2.25 +125 44.4% 6/4 2.50 +150 40.0% 7/4 2.75 +175 36.4% 2/1 3.00 +200 33.3% 5/2 3.50 +250 28.6% How to Find the Best Betting Odds
Your search for the best betting odds should start at the biggest betting sites in the UK. The most generous sites are usually those with the biggest turnovers as they can afford to be generous. However, no matter the site you choose, you will find there is not that much disparity between the best odds and the least profitable. Most bookie’s odds come from central sources that monitor the gambling odds of competitors to make sure they stay profitable. You won’t need to hunt high and low for the best odds, and getting the best odds – while important – should not solely determine which bookie you choose as there are several other factors to consider.
(Not) Against All Odds
If odds have been confusing you in the past, then after reading this page, you should have no problem understanding how do betting odds work. Football odds, cricket odds, horse racing odds … you should be able to understand bookmaker odds and even understand 11/4 odds in decimal (hint: it’s 3.75). Now that you know how to read betting odds, you’ll have no problem placing your sporting bets with confidence.
FAQs
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