Casino odds explained

Casino odds explained in plain English

Every casino bet has two numbers attached to it. One is the probability, which is how often the bet wins over the long run. The other is the payout, which is how much you receive when it does. In a perfectly fair game, the two would balance exactly. In a casino game, the payout is set slightly lower than the probability justifies, and that small shortfall on every bet is how the casino makes its money.

Take a single number at European roulette. There are 37 pockets, so the chance of your number coming up is 1 in 37, or 2.70%. A fair payout would be 36 to 1. The actual payout is 35 to 1. That one-unit gap, spread over the 37 possible outcomes, gives the house its 2.70% house edge. Every casino game works on this principle, though the maths behind cards, dice and slot reels is more involved.

How casino odds are written

Casino games use several ways to express the same idea, and confusing them is a common source of mistakes.

The words ‘to’ and ‘for’ matter. A game paying ‘8 to 1’ returns £9 on a £1 winning bet, while one paying ‘8 for 1’ returns £8. Some games, particularly video poker paytables, use ‘for’ style figures, while table games usually quote ‘to 1’. When comparing two versions of a game, check which style each uses.

How to convert casino odds into a probability

Probability is the most useful format because it lets you compare any two bets directly. Converting is straightforward:

1. Count the outcomes that win your bet. Red at European roulette: 18.
2. Count all possible outcomes. European wheel: 37.
3. Divide winners by total: 18 ÷ 37 = 0.4865.
4. Multiply by 100 for a percentage: 48.65%.
5. To turn ‘true odds against’ into probability, use 1 ÷ (odds + 1). For 36 to 1 against: 1 ÷ 37 = 2.70%.

Card games are trickier because the deck changes as cards are dealt, which is why figures for blackjack and baccarat come from computer analysis rather than a simple count. For roulette, our roulette odds and payouts page lists every bet worked out this way.

True odds vs payout odds: where the house edge comes from

The house edge is the average share of each stake the casino keeps. It can be calculated straight from the gap between true odds and payout odds. The table shows the pattern across several well-known bets, using standard published figures; individual versions can differ, and the game’s help screen shows the figure that applies.

The Tie bet in baccarat shows why the payout alone tells you little. Paying 8 to 1 sounds generous, but the true odds are closer to 9.5 to 1, so the edge is more than ten times that of the Banker bet. Detailed working for each game is published by the Wizard of Odds baccarat guide (opens in a new tab) and its craps section (opens in a new tab).

Expected value: turning odds into pounds

Expected value combines probability and payout into a single figure: the average result of a bet if you could repeat it endlessly. Here’s the working for two £10 bets at European roulette:

• Single number: wins 1 time in 37, paying £350; loses 36 times in 37, costing £10. Expected value = (1/37 × £350) − (36/37 × £10) = £9.46 − £9.73 = −£0.27.
• Red: wins 18 times in 37, paying £10; loses 19 times in 37, costing £10. Expected value = (18/37 × £10) − (19/37 × £10) = £4.86 − £5.14 = −£0.27.

Both bets cost the same on average: 27p per £10, which is 2.70%. That’s the edge expressed in money. Multiply by the number of bets and you have the expected cost of a session. One hundred £10 bets on a European wheel carry an expected cost of about £27, whichever bets you choose. Real results will be scattered around that figure, sometimes far above or below it.

Same odds of losing money, very different sessions

If every European roulette bet has the same edge, why does the choice matter? Because the chance of winning on any one spin varies hugely, which shapes how a session feels. Statisticians describe this spread as standard deviation.

A player backing one number has roughly a one-in-three chance of not winning once in 37 spins, then a single win that roughly restores the balance. A player on red will see wins and losses alternate far more evenly. Over many sessions, both end up near the same expected cost. Slot players meet the same idea as volatility and hit frequency.

What about slot odds?

Slots don’t display odds for each symbol combination. A modern video slot has so many possible outcomes, with features, multipliers and cascading wins, that listing them would be impractical. Instead, the help screen shows the return to player (RTP), the long-run percentage of stakes paid back. A 96% RTP slot has a 4% house edge in the same sense as roulette’s 2.70%. Our RTP explainer covers the details.

Two cautions apply. First, the same slot can run at different RTP settings at different casinos, a practice described in our RTP range glossary entry, so check the figure in the game you’re actually playing. Second, jackpot odds are rarely published; progressive jackpots in particular are very unlikely to land on any given spin. Our guide to progressive jackpots explains how they’re funded.

Casino odds myths

• Myth: the casino tightens the odds when you’re winning. In certified games, outcomes come from a random number generator or physical equipment, and the odds are fixed in the rules.
• Myth: a number that hasn’t come up for a while is due. Each spin is independent; this is the gambler’s fallacy.
• Myth: slots pay more at certain times of day. Nothing in the maths changes with the clock, as we explain in do slots pay more at night.
• Myth: RTP applies to each session. RTP is a long-run average across huge numbers of plays; a single session can land anywhere.

UK rules on odds, fairness and information

Games supplied to licensed casinos in Britain must meet the Gambling Commission’s Remote Gambling and Software Technical Standards (opens in a new tab), which cover random outcomes, game information for players and design features. Our page on RTP display rules covers what return information players should be able to find.

Design rules matter for odds too, because they affect how many bets you place per hour. Since 31 October 2021, slots must take at least 2.5 seconds per spin, and since 17 January 2025 other online casino games must take at least 5 seconds per game cycle. Fewer rounds per hour means less money staked and a lower expected cost per hour, even though the odds per bet are unchanged.

Using casino odds to make better choices

You can’t change the odds of any bet, but understanding them helps you choose games and bets that suit your budget. Pick single-zero roulette over double-zero. Compare blackjack tables on their rules. Avoid high-edge side bets if you want your money to last. Our guide to the best odds casino games ranks games by edge.

Above all, treat the edge as the price of entertainment. Over time the odds favour the casino, and the expected result for players is a loss. Set a budget before you play and stop when it’s spent.

Where to play with the odds explained

These UK-licensed casinos carry a mix of slots and table games; check each game’s help screen for its rules and RTP. Offers checked 5 October 2026; 18+ and terms apply.

• Coral Casino: bet £10 or more on slots after a qualifying deposit to get 100 free spins at 10p each on selected games, worth £10 in total. Accept within 48 hours, use within 7 days, no wagering on winnings. PayPal, Skrill, Neteller, Paysafe and prepaid cards don’t qualify.
• PlayOJO: 80 free spins on Big Bass Bonanza at 10p each, worth £8, with a first deposit of £10 or more; winnings are cash with no wagering. Excludes Northern Ireland.
• Casumo: 50% bonus up to £100 on a first deposit of £20 or more, opt-in required. A £40 deposit brings a £20 bonus; at 10x, that means £200 of wagering within 7 days, with a £5 maximum bet.

Compare every current deal on our latest welcome offers page or browse the guides hub.

18+. Gambling should be entertainment that costs money, not a way to make it. Set a deposit limit before you play: how to set deposit limits. Free, confidential help: National Gambling Helpline 0808 8020 133.