Guide to Casino Game Odds

Last Updated on July 4, 2024 by Jennifer Wright

Learning about online gambling, you’ll come across various terms and complex words. One term that’s likely to pop up more than once is ‘odds’. Odds are a puzzle to even some experienced gamblers; you can never understand them fully.


The problem is that odds form a huge part of gambling. Understanding them makes you stand out from a sea of confused players, all struggling to win wagers because they’re miscalculating odds.

In this guide, you’ll learn everything on casino game odds.

What is Probability?

With the knowledge of probability, you’ll be in a better position to understand odds and how they’re calculated.

At its essence, gambling allows you to predict the outcomes of certain events. Predicting the right outcome means you’ll win some extra money. And in the same vein, making a wrong prediction means you’ll lose money. In each event, there are multiple outcomes.

Let’s take the example of dice rolling. When you roll a dice, you’re facing six possible outcomes. Each outcome has about a 16% chance of happening. There’s an equal likelihood of getting a ‘1’ or a ‘6’. This likelihood is known as probability.

What are odds?

‘Odds’ is a term casually thrown in gambling circles and online reviews. It can sometimes be confusing, especially if maths isn’t your forte.

But you don’t need a deep understanding of Maths to grasp the concept of probability. To give you an idea of what odds are, let’s look at the example of a coin toss.

Every time you toss a coin, you have a 50/50 probability of getting either a heads or tails. Assuming your coin won’t land on its side, there’s an equal chance of either outcome happening. In a casino, you’d expect odds of 2.0 or 1/1. The former represents decimal odds and the latter, fractional odds.

Decimal odds

Popularly referred to as European odds, decimal odds represent a multiple of the total amount that you receive after winning a bet. For instance, placing a wager priced at 3.0, you stand a chance to win 3 times your betting amount. This means you can win £3 for every £1 you bet.

Use the following formulas to calculate your possible returns when using decimal odds:

  • Getting your winning amount: Odds x Stake = winning amount e.g. 2.5 x £10 = £25
  • To get toral profit: (Winning amount) – Stake = profit e.g. (2.5 x £10)– £10 = £15

Fractional odds

These odds feature formats such as 9/1, 7/2, etc. Using them, you can get an idea of your potential returns – if you place a bet worth the second number, you win an amount worth the first number. If we use the second example, you can win £7 if you wager £2.

You can convert these fractional odds to a probability percentage using an easy formula:

Probability (%) = 2 / (1+2), where 1 and 2 are the initial and second numbers, respectively.

When we plug in the 7/2 example, we get a 22.2% probability. We simply entered the figures in the formula to get: 2 / (7 + 2) = 0.22, meaning you there’s a 22% of the outcome happening. Other examples include:

  • 5/1 can be 1 / (5 + 1) = 0.16 – You get a probability of 16%.
  • 7/1 can be 1 / (7 + 1) = 0.12 – You get a probability of 12%.
  • 1/1 can be 1 / (1 + 1) = 0.50 – You get a probability of 50%.
  • 1/6 can be 6/ (6 + 1) = 0.85 – You get a probability of 85%.

Decimal vs fractional odds

Naturally, there are no financial perks in using one format over the other. But, in recent times, bookmarkers have been preferring the decimal odds format over the other. In the past, fractional odds were the clear favourite especially in the UK, but decimal odds have been gaining tractions for two reasons.

Firstly, players can understand decimal odds easier. In horseracing, for instance, bookmarkers are using decimal odds to draw in more customers, making gambling easily accessible to everyone.

Secondly, decimal odds represent both winnings and the stake. Fractional odds, on the other hand, only display the possible winnings. When odds fluctuate slightly, bookies find it difficult to make marginal increases or decreases. And sometimes, these newly-changed odds may form complex fractions that the average player can’t compute easily.

Online casino odds vs land-based odds

For every £1 you bet in a land-based casino, you expect about 88% payouts on average. In contrast, for every £1 you bet in a reputable UK online casino, you expect a 95-97% payout. You might assume that online casinos are generally generous, but this isn’t the case.

Operating an online casino differs slightly to running a land-based one. To put it simply, online sites don’t mind you raking up more wins. They don’t pay rent for their premises, or any other huge bills. Salaries only take up a small percentage of their budget, as they employ fewer workers.

Traditional casinos don’t offer gambling as their sole service; they also offer entertainment and drinks. Contrarily, online sites don’t have to provide these services, so they only focus on gambling. Also, online sites don’t have any space restrictions. This means they can offer as many games as possible. You’ll find thousands of game variants online, compared to land-based casinos that only offer a handful of popular games.

Better yet, the less-known game variations tend to provide better odds for players.

Random Number Generator

Each time you play real-life Blackjack, every hand occurs randomly. This is mainly because the croupier rearranges the cards by shuffling the deck. Playing as a shooter in craps, your dice lands randomly, as it’s up to gravity.

But in online casinos, everything happens on the internet – there’s no physical shuffling of cards or rolling of dices. So how does a casino achieve this randomness, and ensure gaming is fair? Enter the Random Number Generator, or in short, RNG.

The RNG is a program that helps generate sequences of random digits, ensuring that shuffling decks and rolling dices are done randomly. Powered by an extensive sequence of seed numbers, the program is secure against fraudsters and hackers.

Casinos get independent auditors to test the fairness of the program, meaning you’re assured of accurate results whenever you start playing your favourite games. Casinos who’ve passed the accuracy and fairness test often display this fact openly on their websites.

Does the Casino Always Win?

Gambling has a lot of uncertainties, except one: The casino always comes out on top. Casinos, whether land-based or online, are businesses; they must make a profit. They’re not charitable foundations, willing to give free money to the less-fortunate gamblers.

With a business model created to make them as much money as possible, casinos use various tactics to get the edge over the player. One of these tactics is the use of house edges. The house edge is the mathematical advantage a casino has over its customers.

The house edge

Note that the odds you get in online casino don’t represent the actual probability of an event happening. Games have a profit margin added to their odds, ensuring that whether you win or lose, the casino earns its profit in the long run.

This means that the payout you receive if you win your bet is less than the amount you’d receive if the game had ‘true’ odds. The difference between the casino’s odds and an event’s true odds is what’s known as the house edge.

For instance, let’s imagine a slot machine with a house edge of about 4%. This means that whenever you place a bet of £100, the site pockets a profit of about £4.

As we’ve stated earlier, this house edge creates profit for the casino in the long run. Recent studies show that the more hands you win, the less winning amount you’re likely to walk away with, especially if you’re a beginner. This concept can be explained simply: The more wins you get, the more you want to play. And as you increase your playing time, the more likely you are to have occasional losses.

Note that, game developers set the house edges for online games and not online casinos. If an online site tampers with the house edge, then it may face serious consequences, as the act is considered illegal. To the contrary, land-based casino games’ RTPs can change either positively or negatively due to various reasons.

The RTP explained

Return to Player is the percentage of money a casino’s game returns to players on average. For instance, if a slot game’s RTP is 92%, for each £100 players bet on it, the game returns an average of £92. This figure, though, doesn’t mean the slot machine will always pay out £92 when you wager £100. It means, however, that if you were to play with infinite spins, you’d get this average.

RTP applies to all games, both in land-based and online casinos. Getting the RTP is easy, once you have the house edge. Both percentages, when summed together, should equal 100%. You can use the formula below:

  • RTP = 100% – House Edge
  • E = 100% – RTP (H.E represents the house edge)

For instance, if a roulette game had a 94% RTP, then its house edge would be 6%(100-94). Or if a craps’ house edge would be 13%, then its RTP would be 87%(100-13)

Casino games with the best odds


Even though you need some luck to win big in Blackjack, just like in other casino games, you mostly need the skill to rack up consistent wins and make a fortune. That’s why Blackjack has some of the best odds in UK casinos, offering RTPs of about 98% on online sites. Learn how to play blackjack with our comprehensive guide.

If you devise a well-thought-out strategy, you can lower the card game’s house edge to 0.12%. Considering Blackjack’s house advantage increases by 0.02% whenever you add a deck, you can choose to focus on single or double deck card games. You can even drop the house edge by -0.13% by playing in games where the croupier stands on 17.

Some of the blackjack variations with favourable odds include:

  • Spanish 21
  • Pontoon
  • Blackjack Switch
  • Atlantic City


Originating from Europe, Roulette is a game rich in history. Not only does it have one of the most favourable odds in casino gaming, but it’s also one of the simplest to play. You only need to wager on your favourite numbers. The dealer then spins the roulette wheel, and if your chosen number appears, then you win your bet.

Sticking with the common numbers red and black gives you a 50-50 probability of walking away with some profit. There’s however one catch: the extra 0 or 00 makes it harder to have an even probability of winning.

American Roulette has slightly worse odds, with its two zeros on the roulette wheel, while European Roulette gives you a better chance of getting a win. The extra zero in the former gives it a house edge of over 5%, a big difference compared to the latter with a 2% house edge.

You can implement a strategy like the Martingale System to get an even better advantage. This a betting strategy that requires you to double your betting amount after each loss. Whether it’s a profitable tactic is anybody’s guess. That said, Roulette should be among your top picks when you’re looking for favourable casino odds. Brush up your skills by reading our how to play roulette guide.


Just like Roulette, Craps has been a staple in the casino industry for years, passed from one generation to another. And also just like Roulette, you can get odds nearing 50-50 with the dice game. Understandably, it frightens most novice players, with all the boxes on one table. The fact that it has loads of different betting styles doesn’t help either.

But if you can eliminate your mental block, you can make some decent profit from the dice game.

Coming up with a sensible strategy can help you improve your odds further and even reduce your house edge to as low as 1.5%.

Games with the worst odds

Online Slots

Without a doubt, slots are among the most popular games in casinos. Players find it hard to resist the exciting themes, immersive storylines, and glittering lights. But if you’re an astute gambler, you might want to step away from the glamorous slot machines.

A nightmare to odds’ enthusiasts and math lovers, slots have one of the worst odds in online casinos. Run by complex RNGs, they have various versions, and each game’s mechanics differ to some extent.

Calculating the casino game’s odds can be a grind. For instance, 5-wheel slot machine with 10 symbols and 20 pay lines can produce over 30 million varying symbol combinations. In contrast, video poker has about 2.5 million potential combinations, and single deck blackjack has about 1320 possible starting hands.

Wheel of Fortune

Wheel of Fortunes continues to be a major draw in land-based casinos and in some online sites. The game’s huge popularity can be attributed to TV shows romanticizing the game. What you don’t know, though, is that it has one of the worst odds in the industry. At 25%, the game’s house edge beats almost all the other casino game’s house advantages. Worse yet, walking away from the game empty-handed is a huge possibility, as it doesn’t offer any consolation rewards, unlike in the gaming shows.

Progressive Odds

Progressive slots can be very exciting. They offer mouth-watering winning amounts. They are constantly increasing in value, as each player joins the game. And, most importantly, they have enjoyable gameplay. When it comes to odds, though, these jackpot games paint a picture of a very risky casino game. Your chances of winning a progressive jackpot are super-slim compared to other games on this guide.

Players contribute to the Jackpot’s overall winning amount. This means that the game’s players share the odds, making it challenging to compute your probability of winning.

Understanding the grind

Gamblers dread the grind. When you’re falling into the pit that’s the grind, your betting strategy goes out the window, your confidence nose-dives, and your bankroll plummets. If you’re a novice player, you might be experiencing the grind because you’re approaching the house edge wrongly.

Note that your house edge doesn’t apply to your entire bankroll, and rather your betting amount. If you have the opposite assumption, you might be playing low house edge games but for a very long time. So, how’s this a bad approach?

When playing for a long time, eventually all your bets will exceed your bankroll. The bets you make in one hour of playing time may come to surpass your intended betting amount. For instance, you might play a game with a relatively low house edge like roulette. Assuming your roulette version has a 3% house edge, you might start betting with a £100 account balance.

With the wrong approach, you might bet for some hours, thinking you’ll only have about £3 to lose. What you don’t know is that the house edge only applies to your bet amount. Now assume you place £5 wager on all roulette wheel’s spins. Assuming the wheel spins at least 50 times every hour, you might be wagering at least £250 with each passing hour.

Given Roulette is mostly a game of chance, you might be winning some wagers and losing others. If the game’s house edge comes into play perfectly, you might be looking at a £30 loss after 4 hours of game time – you’ve lost ten times more than you had anticipated.

Worries about odds

Playing in the same casino is often a major worry for some players. You might think that being a regular customer might impact your odds negatively – this assumption couldn’t be further from the truth. All gamblers, whether amateurs or pros, have the same probability of winning.

Another worry, the casino tampering with odds to favour them, also isn’t true. While there’s a slight possibility that a rogue casino might manipulate a game’s algorithm to get an upper hand, you’ll rarely find any licensed casino engaging in such illegal activities. The consequences outweigh the benefits – casinos risk getting their licence revoked and closing shop permanently.

That said, you’re better off playing in licensed casinos. Always check for a licence on the casino’s main website.


Which casino game has the best odds?
Arguably, Blackjack has some of the most favourable odds in UK online gambling. Firstly, at a 98% payback percentage, it leads other popular casino games that have, on average, a 96% payback percentage.

Secondly, it isn’t entirely based on luck. This means you can increase your chances of getting better odds by devising a sensible strategy. Compared to a game like bingo, for example, blackjack allows you to have some influence on the game, and if you’re smart enough, you make some profit.

Are RTP and house edge different?
Yes, they are. RTP is the percentage of money a casino pays out to you on average for all your wagers. House edge, on the other hand, is the percentage of your betting amount that the casino gets as profit. When you add these two percentages together, you should get a total of 100%. If a casino game has an RTP of 89%, you can instantly know its house edge is 11%.
Are my game's odds affected by the house edge?
To put it simply: yes it does. As we’ve explained in the guide above, casinos generally don’t present the ‘true’ odds of an outcome happening. They have to factor in their profit in these odds so that regardless of whether you win or lose, the casino will pocket some profit in the long run.
Why do slot games have poor odds?
Firstly, slots are games of chance; you don’t have any influence over the spinning reels. Whether you win or lose is out of your control. Unlike Blackjack, you can’t come up with any strategies that will give you an edge over the house. You only have to place your wager and wish for luck to be on your side.

Secondly, as we’ve mentioned before, a single slot machine can produce millions of potential combinations. And the more the possible outcomes, the poorer the odds.

Jennifer Wright is an online casino and slots writer since 2010. She has an eye for detail and take pride in her in-depth analysis of new casino sites that enter the UK market. A regular at iGaming conferences and events, she is also a keen follower of industry news. In her downtime, she is an avid gamer and regularly takes part in esports tournaments. Jennifer currently resides in the north of England.