Blackjack Strategy Calculator
Calculate the optimal blackjack move based on your hand and the dealer upcard using mathematically proven basic strategy.
Blackjack Strategy Calculator
Calculator
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Formula: Optimal Action = BasicStrategy[HandType][HandTotal][DealerUpcard]
Worked example — Optimal Play: Surrender (or Hit if unavailable) | Dealer bust chance: 23.2%
Formula
Optimal Action = BasicStrategy[HandType][HandTotal][DealerUpcard]
Basic strategy is derived from computer simulations of millions of blackjack hands. For each combination of player hand (hard, soft, or pair) and dealer upcard, the expected value of every possible action is calculated, and the action with the highest expected value is selected.
Worked Examples
Example 1: Hard 16 vs Dealer 10
Problem:You hold a 10 and a 6 (hard 16) against a dealer showing 10. What should you do?
Solution:Hand type: Hard 16 Dealer upcard: 10 Basic strategy lookup: Hard 16 vs 10 = Surrender (R) If surrender unavailable: Hit (H) Dealer bust probability with 10: 23.2% Player bust if hitting: 61.5% Expected loss standing: ~48% Expected loss hitting: ~54% Expected loss surrendering: 50% (but you save half your bet)
Result:Optimal Play: Surrender (or Hit if unavailable) | Dealer bust chance: 23.2%
Example 2: Soft 18 vs Dealer 9
Problem:You hold an Ace and 7 (soft 18) against a dealer showing 9. What is the correct play?
Solution:Hand type: Soft 18 (Ace + 7) Dealer upcard: 9 Basic strategy lookup: Soft 18 vs 9 = Hit (H) This is counterintuitive since 18 seems strong But dealer average hand with 9 showing is ~18.5 Hitting cannot bust (soft hand reverts to hard if over 21) Hitting improves the hand more often than standing holds
Result:Optimal Play: Hit | Standing on soft 18 vs 9 is a common mistake
Frequently Asked Questions
What is basic blackjack strategy and does it really work?
Basic strategy is a mathematically optimal set of decisions for every possible blackjack hand combination. It was first developed in the 1950s by Roger Baldwin and later refined by Edward Thorp using computer simulations of millions of hands. Basic strategy reduces the house edge to approximately 0.5 percent, making blackjack one of the best odds games in the casino. Without basic strategy, the average player faces a 2 to 5 percent house edge. The strategy accounts for the probability of every possible card draw, the dealer rules, and expected values of hitting, standing, doubling, and splitting. While it does not guarantee winning any individual hand, it maximizes your long-term expected return over thousands of hands played.
When should you double down in blackjack?
Doubling down is optimal when you have a mathematical advantage on the next card. The strongest double down situation is a hard 11 against any dealer card, because you have the best chance of making 21. With hard 10, double against dealer 2 through 9. With hard 9, double against dealer 3 through 6. For soft hands containing an ace, double with soft 16 through 18 against dealer 4 through 6, and soft 17 against dealer 3 through 6. Never double down on hard 12 or higher because the bust risk is too great. Doubling down effectively lets you double your bet when the odds temporarily favor you, which is why knowing the correct situations is crucial for reducing the overall house advantage.
Should you always split aces and eights in blackjack?
Yes, splitting aces and eights is one of the most fundamental rules of basic strategy. Always split aces because each ace gives you a starting hand of 11, the strongest starting position for any hand. Always split eights because a hard 16 is the worst possible hand in blackjack, and splitting gives you two chances to build competitive hands starting from 8. Conversely, never split tens because 20 is already an excellent hand that wins the vast majority of the time. Never split fives because a hard 10 is a strong doubling opportunity. Pairs of fours should generally not be split either, as a hard 8 is better played as a single hand. Splitting decisions for other pairs depend on the dealer upcard.
How does the number of decks affect blackjack odds?
The number of decks significantly impacts the house edge in blackjack. A single-deck game with standard rules has a house edge of about 0.17 percent, while an eight-deck shoe increases it to approximately 0.65 percent. More decks reduce the effectiveness of doubling down on 11 because there are proportionally fewer tens in the remaining cards relative to total cards. The probability of natural blackjack decreases slightly with more decks. Card counting becomes more difficult with more decks because individual card removals have less impact on the remaining composition. Most casinos use six or eight decks specifically to combat card counting and increase their edge. However, basic strategy adjustments for multi-deck games are minor, and the core strategy decisions remain largely the same.
What is surrender in blackjack and when should you use it?
Surrender is a blackjack option that allows you to forfeit half your bet and give up your hand before playing it out. Late surrender, the most common form, is available after the dealer checks for blackjack. Basic strategy recommends surrendering hard 16 against dealer 9, 10, or ace, and hard 15 against dealer 10. These specific hands have such poor expected values that losing half your bet immediately is mathematically better than playing them out. Surrender reduces the house edge by approximately 0.07 percent when available and used correctly. Many casinos do not offer surrender, and some only offer it on certain table minimums. Early surrender, available before the dealer checks for blackjack, is extremely rare but very valuable to the player.
What is the difference between a hard hand and a soft hand?
A soft hand contains an ace still counted as 11, so it cannot bust with one more card; the ace simply drops to 1 if the total would exceed 21. Ace-6 is a soft 17 and can be hit safely, whereas a hard 17 made of 10-7 has no such cushion. This is why basic strategy hits or doubles many soft totals that would be stood on as hard totals. As soon as the ace is forced down to 1, the hand becomes hard and the normal bust-risk rules apply.
How does the dealer hitting soft 17 change the odds?
In an H17 game the dealer must draw on soft 17 rather than standing, which gives the house a second chance to improve a mediocre total. This shifts the edge toward the casino by roughly two tenths of a percentage point compared with an otherwise identical S17 game. It also alters a handful of basic strategy decisions, most notably doubling soft 18 and 19 against a dealer ace and doubling 11 against an ace. Always check the felt for the H17 or S17 marking before choosing a table.
Why is insurance considered a bad bet in blackjack?
Insurance is a side bet that the dealer's hole card is a ten-value card, paying 2 to 1. Break-even requires that card to be a ten more than one time in three. In a full deck only 16 of the 52 cards are ten-valued, which is under 31 percent, and your own cards typically remove ten-value cards from the pool as well, pushing the true chance even lower. Taking even money on your own blackjack is the same wager in disguise. The bet only becomes profitable when a card counter knows the remaining shoe is unusually rich in tens.
What is the difference between basic strategy and card counting?
Basic strategy is a fixed lookup of the highest expected-value action for each player total against each dealer upcard, and it never changes during a shoe. Card counting tracks how the composition of the undealt cards drifts as low and high cards are removed, usually with a balanced system such as Hi-Lo where 2 through 6 count plus one and tens and aces count minus one. Dividing the running count by the decks remaining gives the true count, which is used to raise bets when the shoe favours the player and to deviate from a few basic strategy decisions.
Why does a 6 to 5 blackjack payout matter so much?
A natural blackjack traditionally pays 3 to 2, returning 1.5 units of profit per unit wagered. Tables that pay only 6 to 5 return 1.2 units on the same hand. Because a natural appears in roughly one hand in twenty-one, that shortfall adds well over a full percentage point to the house edge, more than tripling the roughly half a percent edge a basic strategy player faces at a 3 to 2 table. No amount of correct play compensates for it, so avoiding 6 to 5 tables is the single most valuable rule-selection decision in blackjack.
References
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
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