Blackjack rules, basic strategy and house edge

On this page

How the game works
Basic strategy
The house edge and the rules that change it
Side bets
Common myths
What to check at a licensed casino
Play within your limits

Blackjack is the one common casino game where your decisions change the house edge. Played well, under good rules, it costs you about half a percent of what you bet. Played badly, or at a table with poor rules, the cost can be several times higher. Here is what you need to know.

How the game works

You play against the dealer, not against other players. The aim is to finish with a hand closer to 21 than the dealer’s without going over.

Number cards count at face value. Jacks, queens and kings count as 10. An ace counts as 1 or 11, whichever helps the hand.
You and the dealer each get two cards. Usually one dealer card is face up.
An ace with a 10 value card as your first two cards is a blackjack. It beats any other 21.
You act first: hit (take a card), stand, double down (double your bet and take exactly one card), or split a pair into two hands.
If you go over 21 you bust and lose immediately, even if the dealer later busts too. This is the main source of the house edge.
The dealer then plays by fixed rules, typically drawing until reaching 17 or more.

A winning hand pays 1 to 1. A blackjack traditionally pays 3 to 2. Ties are a push and your stake is returned.

Basic strategy

Basic strategy is the mathematically best decision for every combination of your hand and the dealer’s up card, worked out by computer simulation of millions of hands. It does not guarantee you win. It means you lose as little as possible over time.

The full strategy fits on one chart, and many players keep one open while they play online. The key ideas:

Hard 17 or more: always stand.
Hard 13 to 16: stand if the dealer shows 2 to 6, hit if the dealer shows 7 to ace.
Hard 12: stand against 4, 5 or 6; otherwise hit.
11: double against most dealer cards.
10: double against 2 to 9.
Pairs: always split aces and eights. Never split tens or fives.
Soft hands (a hand with an ace counted as 11): soft 18 or lower usually needs a hit or a double, depending on the dealer card. Standing on soft 17 is a common mistake.
Insurance: do not take it.

Exact plays change slightly with the number of decks and table rules, so use a chart that matches your table.

The house edge and the rules that change it

With basic strategy and common rules (several decks, blackjack pays 3 to 2, doubling after splits allowed), the house edge is around 0.5%. Individual rules move that number:

Blackjack pays 6 to 5 instead of 3 to 2: adds roughly 1.4% to the edge. This is the single most costly rule change.
Dealer hits soft 17 instead of standing: adds about 0.2%.
No doubling after a split: increases the edge slightly.
Doubling restricted to 10 or 11 only: increases the edge slightly.
Late surrender offered (give up half your bet after seeing the dealer’s card): lowers the edge slightly, if you use it correctly.
Fewer decks: generally a little better for the player, all else equal.

Worked example: 3 to 2 against 6 to 5

You bet 10 units and are dealt a blackjack. At 3 to 2 you win 15. At 6 to 5 you win 12. You lose 3 units each time you get a blackjack.

You get a blackjack in roughly 1 hand in 21, which is about 4.75% of hands. So on average the 6 to 5 rule costs you 3 x 4.75%, or about 0.14 units per 10 unit hand. That is about 1.4% of your stake. It nearly triples the cost of playing compared with a good 3 to 2 table.

Worked example: why insurance is a poor bet

When the dealer shows an ace, you are offered insurance: a side bet of half your stake that pays 2 to 1 if the dealer has blackjack. In a six deck game, after one ace is out, 96 of the remaining 311 cards are worth 10, so the chance the dealer has blackjack is about 30.9%. A bet paying 2 to 1 needs better than 33.3% to break even. The result is a house edge of roughly 7% on the insurance bet. Even money on your own blackjack is the same bet in disguise.

Side bets

Many tables offer side bets on pairs, poker style combinations or the dealer busting. They pay large amounts, but their house edge is usually much higher than the main game. The rules panel normally lists the RTP of each side bet. Compare it with the main game before you play one.

Common myths

“I’ve lost five hands in a row, a win is coming.” This is the gambler’s fallacy. Past hands do not make the next one more likely to win.
“Martingale works in blackjack.” Doubling after losses does not change the edge on any hand. It also clashes with doubling down and splitting, which can leave far more money on the table during a losing run than you planned. Table maximums end the sequence before it can recover large losses.
“Bad players at the table cost me money.” Other players’ decisions change which cards you get, but they are as likely to help you as hurt you. Over time they do not change your edge.
“Card counting works online.” RNG blackjack usually reshuffles after every hand, so there is nothing to count. Live tables generally use multi-deck shoes with continuous shufflers or early reshuffles, which removes most or all of the benefit.
“Always assume the dealer has 10 in the hole.” It is a rough rule of thumb, not a strategy. Use the actual basic strategy chart.

What to check at a licensed casino

Blackjack payout. Look for 3 to 2, often printed on the table felt or in the rules. Avoid 6 to 5 tables.
Dealer rule on soft 17. Stands on soft 17 is better for you than hits soft 17.
Doubling and splitting rules. Check whether you can double after splitting and on which totals.
Number of decks and surrender. Both are usually listed in the rules panel.
RTP figure. Most games show an RTP assuming optimal play. Your actual return will be lower if you do not follow basic strategy.
Table limits. Make sure the minimum fits your budget, remembering that doubles and splits need extra money.
Licence. Only play where the casino is licensed for your market. See licensing.

Play within your limits

A low house edge is still an edge, and long sessions add up. Decide your budget and session length before you start, keep your stake steady, and walk away when you hit your limit. If gambling is causing problems, visit our responsible gambling page for tools and support.