Strategy Center: House Edge, EV & Probability

House Edge Explained

House edge is the built-in mathematical advantage the casino holds over the player in any given game, expressed as a percentage of each bet. It's not a trick or a rigged outcome — it's simply how the payout structure is designed, and it's directly tied to a game's RTP:

A slot with a 96% RTP has a 4% house edge: over a very large number of spins, the casino keeps 4% of everything wagered on average. House edge is a long-run average, not a guarantee for any single session — you can win in the short term on a game with a high house edge, and lose on a game with a low one. What it does tell you is which games are mathematically friendlier to play over time.

Sportsbooks work differently. A betting line has no RTP; instead, the bookmaker builds a margin (also called the overround or vig) into the odds. You can measure it by adding up the implied probabilities of every outcome: if both sides of a bet are priced at −110 (1.91), each implies 52.4%, so the total is 104.8%. The extra 4.8% is the bookmaker's margin. See how odds work for the conversions.

For the house edge on specific casino games, see our house edge table.

Expected Value (EV)

Expected Value tells you, on average, how much a bet is worth before you place it — factoring in both the probability of winning and the size of the payout. It's the single most useful concept for comparing whether a bet is mathematically favorable or unfavorable.

Here, "Amount Won" means your net profit, not including the stake you get back.

A simple example: a bet with a 50% chance to win $100 and a 50% chance to lose your $50 stake has an EV of (0.5 × $100) − (0.5 × $50) = $25. A positive EV means the bet is favorable on average; a negative EV — which describes nearly every standard casino game and sportsbook line, by design — means you're expected to lose money over time even if any single bet can go either way.

Two real examples:

• European roulette, $10 on a single number. The ball has a 1 in 37 chance of landing on your number, which pays 35 to 1. EV = (1/37 × $350) − (36/37 × $10) = $9.46 − $9.73 = −$0.27. That's −2.7% of your stake — exactly the game's house edge.
• A $100 bet at −110 on an even matchup. If each side really has a 50% chance, a win pays $90.91. EV = (0.5 × $90.91) − (0.5 × $100) = −$4.55, or about −4.5% of your stake. That's the cost of the bookmaker's margin.

Neither loss shows up on any single bet — you either win or lose the whole thing. It shows up as the average across many bets.

Probability and Variance

Probability is the likelihood of a specific outcome occurring, usually expressed as a percentage or a fraction. Variance describes how much actual results swing around the expected average — two games can have the exact same RTP and completely different variance profiles.

• Low variance Frequent, smaller wins that stay close to the expected average. Your bankroll moves in small, predictable steps.
• High variance Infrequent but larger wins, with long stretches of losses in between. Short-term results can look nothing like the long-term average.

Understanding variance matters for bankroll management: a high-variance game can wipe out a small bankroll long before the "long run" ever arrives, even if its RTP is favorable. For more on how volatility interacts with RTP, see our iGaming basics guide.

RTP isn't how often you win. A slot's RTP tells you what share of all money wagered it pays back over time. Its hit frequency tells you how often a spin returns anything at all. A high-volatility slot might have a 97% RTP but pay out on only one spin in five; a low-volatility slot with a 94% RTP might pay out on one spin in three. A higher RTP means a lower long-run cost, not more frequent wins.

Common Myths and Fallacies

• The Gambler's Fallacy The belief that a losing streak makes a win "due," or that a random outcome that hasn't happened in a while becomes more likely. Every independent spin, hand, or bet has the same odds regardless of what came before it.
• Hot and Cold Streaks Players often read meaning into short sequences of wins or losses that are, statistically, exactly what randomness looks like. A genuinely random process still produces streaks.
• Betting Systems (e.g. Martingale) Progressive staking systems that double your bet after a loss don't change the underlying house edge — they just change how quickly you can hit a table limit or run out of bankroll while chasing losses. Take the Martingale on red in European roulette, starting at $10. After six losses in a row, your next bet is $640 just to win back $10 — and you're already down $630. Losing six red bets in a row happens about 1.8% of the time (19/37 to the sixth power), which sounds rare but comes up regularly over hundreds of spins. Table limits often stop the progression before it can recover. See why the Martingale system fails for the full breakdown, including the expected-value math.
• "Due" Numbers In games like roulette, no number, color, or symbol is ever "overdue." Each spin is a fully independent event with no memory of previous outcomes.
• "A 96% RTP means I'll get 96% back." RTP is an average across millions of spins. Your session can end far above or far below it.
• "Near misses mean a win is close." Two jackpot symbols and a blank is just a losing spin. The RNG doesn't get "closer" to a result. (In Great Britain, slots are no longer allowed to celebrate losses as if they were wins.)
• "The casino tightens a slot after I win." At licensed casinos, a game's RTP is set and certified in advance; it can't be changed for individual players or in response to results.
• "Bonuses are free money." Wagering requirements mean bonus funds are played through the house edge before you can withdraw. See how wagering works.

Where Strategy Actually Helps

No strategy removes the house edge. But in some games your decisions change how big that edge is — and in every game, your choice of bet does.

• Blackjack: Basic strategy — the mathematically best play for every hand — cuts the house edge to around 0.5% at typical tables, compared with 2% or more playing on instinct. Choose tables that pay 3:2 for a blackjack, not 6:5.
• Casino poker and video poker: Published strategy charts reduce the house edge in the same way.
• Choosing the bet, not just the game: In baccarat, the Banker bet (1.06%) costs far less than the Tie bet (about 14.4%). In roulette, European or French wheels cost less than American.
• Sports betting: Compare odds across more than one licensed sportsbook ("line shopping"). Getting 2.00 instead of 1.91 on the same bet cuts the margin you pay without changing anything else.
• Bankroll and time limits: They don't change the edge, but they control how much it can cost you. See bankroll management.

Slots, roulette and crash games offer no decisions that change the house edge. The only "strategy" there is choosing a game with a higher RTP and deciding in advance how much you're willing to spend.

Working Out the Numbers Yourself

Every formula on this page is simple enough to work out with a phone calculator: all you need is the game's stated RTP or the bet's odds. We show the math rather than hiding it inside a tool, so you can check any number yourself. For bonuses, where the arithmetic gets fiddlier, use our wagering requirement calculator. If a platform won't disclose a game's RTP, treat that as a red flag in itself.

Frequently Asked Questions

• What does house edge mean? It's the casino's built-in average advantage, expressed as a percentage of each bet. A 2.7% house edge means that, over many bets, the casino keeps $2.70 of every $100 wagered on average.
• What is expected value in gambling? Expected value (EV) is the average amount you win or lose per bet if you placed it many times. Almost every casino bet and sportsbook line has a negative EV by design, which is how operators make money.
• Does the Martingale system work? No. Doubling your bet after every loss doesn't change the house edge. It trades many small wins for occasional very large losses, and table limits often stop you before you can recover. See why the Martingale system fails for the full numbers.
• Is there a strategy that beats slots? No. Slot outcomes are decided by an RNG and there are no decisions that change the house edge. The only choices that matter are picking a game with a higher RTP and setting a budget in advance.
• What's the difference between RTP and hit frequency? RTP is the share of all money wagered that a game pays back over time. Hit frequency is how often a spin returns anything. A game can have a high RTP but pay out rarely, and vice versa.
• Why do I keep losing if the house edge is only a few percent? Because of variance: in the short run, results swing far above and below the average. And because you usually re-bet your winnings, the house edge applies to the total amount you wager, which can be many times your starting balance.

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