Casinos know better than anyone how changing the rules of blackjack will affect your odds of winning. The house edge is built into the rules of the game deliberately. So although 21 is one of the rare games where the house advantage is not fixed, casinos continue to find a way to tweak the rules of blackjack to keep their house edge intact.

What is the house advantage? Simply put, it is the profit margin built into the casino’s gaming operations to make sure they make money. Most casino payouts pay less than true odds (the probability of an event occurring) so that the casino ensures its cut. The most often used example is the roulette wheel. American roulette has 36 numbered spaces plus zero and double zero. Therefore, your true odds of number 15 being the next number is 1/38.

So place your bet on number 15, but if you win, the casino is going pay you 35 to 1 (if you bet $1, your payout will be $35). The difference between your payout and true odds is the house advantage.

Unlike most casino games, blackjack is different in the sense that the odds are not fixed. (The casino odds never change on a roulette wheel). The odds at blackjack depend on what cards have already been dealt, the number of decks being dealt, and the house rules. Where you play makes a difference to your odds of winning, and that is because not every blackjack table has the same rules. Some casinos structure their rules to increase their edge.

At casinos in Connecticut, for instance, the house rules for blackjack include the dealer stays on soft 17, players can double down after splitting pairs, and surrender is available. These rules are reasonably advantageous to the player. Surprised?

In Las Vegas, many casinos have tighter rules and the intention is to increase the house advantage. So they enforce rules that are not quite as good for players. That includes the dealer hitting on soft 17, and surrender is not available. Another trick is to install continuous shuffling machines that randomize the cards and speeds up the game. (The randomization makes it hard to count cards because you never know if you have seen the entire shoe). Though the house advantage is actually less on machine shufflers, the game is faster and you are going to place more bets and catch up to the house advantage quickly.

Las Vegas casinos do make some concessions to the players. In high rollers pits (where the action can be as little as $50/$100 per bet) the rules are often more favorable than in the main pit. And there is no automatic machine shuffler to be found because casinos know that serious players won’t play at a table where they are installed.

Smart players, card counters, and high rollers often know which rules are the least advantageous to the player. They are:

a) When the dealer hits a soft 17

b) When you aren’t allowed to double after splitting

c) When surrender is not allowed

d) When you can only double on a hand of 10 or 11

Each of these variations on the rules increases the house advantage, which means they make it that much harder for the player to walk out the casino a winner.

Knowing that, players are on the lookout for blackjack tables with favorable rules. So casinos have pulled other tricks to keep their edge. They have installed games that look like blackjack but play by greatly different rules, like Spanish 21. They also offer side bets on the blackjack table like Match the Dealer and Triple 7’s. (All with a high house edge). The newest trick is to change the payout on a blackjack. At single deck games, players now find the payout for blackjack at many casinos is now 6-to-1 instead of 3-to-2. That means for every $5 you bet, you are only being paid $6 on a blackjack. Instantly, the casinos have taken away one of the biggest advantages to blackjack players.

Casinos won’t stop varying the rules so the payouts are in their favor, but by knowing how the rules affect the house advantage, a player can still come out a winner.

Brian Jamie is the author of the Philosophy of BJ series. His most recent book, The Philosophy of BJ on 21 is available for download at philosophyofbj.com