The game we know as blackjack has been centuries in the making, with influences  from Italian, French, Spanish and British games, along with some wrinkles added in the United States.

The result has been a collection of optional rules that are added or subtracted as the proprietor sees fit.

That goes for online blackjack just as much as live blackjack. The game you see at one online casino or live casino is not necessarily the same as the one you'll see a click away or a street away.

Some  basics remain in force. Card values remain the same. The need to beat the dealer without going over 21 remains the same, as does the starting point of two cards from which you can hit, stand, split pairs or double down.

But beyond the basics, there's a long list of optional blackjack rules. Some are good for players and reduce the house edge. Others are designed to increase the house edge. Those make blackjack tougher on players.

It's up to you to check out rules before you play and decide whether the game at hand is one you want to play. Usually, the effect of rules working together will yield a game with a house edge of less than 1% against a basic strategy player. Many games have edges of less than half a percent, and if you're lucky, you might find something very close to an even game.

Let's look at some of the most common rules variations.

Number of Decks

Six-deck games are the most common, but it's possible to find one-, two- and eight-deck games. Some live games with automatic shufflers even use four or six decks.

If all other rules are equal, a single-deck game has a house edge about half a percent lower than a six-deck game. However, a single-deck game can have a house edge higher than games with more decks (more on that below).

That aside, why does adding decks increase the house edge? Because with more decks, two-card 21s, or blackjacks, become less common. Players get a bonus payoff on blackjacks, so it helps players to have more frequent blackjacks.

Imagine your first card is an Ace. In a single-deck game, 16 of the remaining 51 cards, or 31.4%, are 10 values that would complete a blackjack. In a six-deck game, 96 of the remaining 311 cards, or 30.9% are 10 value. 

Flip that around and imagine your first card is a 10 value. With one deck, four of the other 51 cards, or 7.8%, are Aces. With six decks, 24 of 311 cards, or 7.7% are Aces.

With either start, the percentages tell us blackjacks are more common with fewer decks.

Similarly, with fewer decks, you’re more likely to draw a 10 in double-down situations. If you have 6-5 in a single-deck game, 16 of the other 50 cards, or 32%, are 10 values that will give you 21. In a six-deck game, it’s 96 of 310 cards, or 31%. You’ll get that wished-for 10 on your double downs more often with fewer decks.

Blackjack Chips

The Big Bad: 6-5 Payoffs on Blackjacks

Traditionally, blackjacks pay 3-2, provided the dealer doesn't also have a blackjack. For a $10 bet, the payoff is $15.

In the last couple of decades, there has been a rise in games that pay only 6-5. For a $10 bet, your blackjack wins only $12.

That's a huge difference, one that adds 1.4% to the house edge. Given the entire edge against a basic strategy player is measured in tenths of a percent, a 1.4% edge-padder is a killer for players.

That's a deal breaker. If you see a 6-5 payoff on blackjacks and not the traditional 3-2, look for a different game or another place to play.

Other Rules

The effects of other common variations aren't as large as the number of decks or the blackjack payoffs, but they're still important. Several may or may not be in effect at the same table. Their cumulative effect can be large.

Make sure you know which of these common rules are being used.

  • Dealer hits or stands on soft 17 – It's better for players if the dealer stands on soft 17.  If the dealer hits, he can't bust soft 17 in one card and he gets a chance to beat your 17 or better. Hitting soft 17 increases the house edge by about two-tenths of a percent.
  • Player may double down on any first two cards versus player may double down only on specific hands – It's best for players to have more options as long as the players take their time to learn basic strategy and know how to use the options.

If the casino permits double downs only on hard totals of 9, 10 or 11, that increases the house edge by about a tenth of a percent. If it restricts doubles to hard 10 or 11 -- eliminating the 9 as well as all soft totals, it increases the house edge by two-tenths of a percent.

  • Player may or may not double down after splitting pairs – After you split a pair, if the draw gives you a two-card total of 11, or sometimes 10 or 9, you want the option to double down. If the casino doesn't permit that play, the house edge increases by .14%.
  • Players may split pairs, once, twice or three times – If you split a pair of 8s and then draw a third 8, creating another 8-8 hand, your best play is to split again. If the casino doesn't allow resplits, it increases  the house edge.

In the best games, you can split up to three times to make a total of four hands. If you can split only twice, it adds one-hundredth of a percent to the edge. If you can split only once, it adds a tenth of a percent, and if splits aren't allowed at all it adds six-tenths of a percent.


Cumulative Effect of Rules

It's not hard to put together a combination of rules in which a game with more decks has a lower edge. For one thing, blackjack payoffs have a bigger effect than the number of decks. If you know nothing else about the games but know a single-deck game pays 6-5 on blackjacks while a six-deck game pays 3-2, you're better off at the six-deck game.

Even with 3-2 pays on both games, the six-deck game can be better if it has better auxiliary rules. Let's say a single-deck game has the dealer hit soft 17. You can double down only on hard 10 or 11, may not double after splits, and may split pairs only once. The house edge against a basic strategy player is 0.45 percent.

What about a six-deck game in which the dealer stands on all 17s, you may double on any first two cards, including after splits, and may split pairs up to three times. The house edge is 0.40%, lower than the edge on the single-deck game. 

It's the full package of rules that matters, not just the number of decks.

For nearly 25 years, John Grochowski has been one of the most prolific gaming writers in the United States. He’s been ranked ninth by GamblingSites among the top 11 gambling experts at Gambling Sites and his Video Poker Answer Book was ranked eighth among the best gambling books of all time.