What Blackjack Mistakes Cost You

Most blackjack players know a few rules and guess the rest. The guesses feel harmless because each one only comes up now and then. This page measures them. For each common mistake it shows the expected value of the correct play, the expected value of the mistake, and the difference, in cents per dollar bet.

Expected value is the average result of a play if you made it thousands of times. A value of -41.5 cents means that, on average, the play gives back 41.5 cents of every dollar you put on it. When every option loses, the right play is simply the one that loses least.

The mistakes, ranked by cost

The most expensive mistakes are the timid ones

The two costliest entries on the list are both failures to put more money out when the odds favour you. Not doubling 11 against a dealer 6 gives up 33.4 cents of every dollar on the hand. Splitting a pair of 5s against a dealer 6, instead of treating them as a 10 and doubling, gives up 45.1 cents.

These are the hands where you are a strong favourite. Doubling is the only bet in blackjack you choose to make, and the chart asks for it exactly when the cards are on your side. Skipping it does not avoid risk; it leaves your best opportunities only half funded.

Hitting hard 17 and splitting 10s

Hitting a hard 17 against a dealer 10 costs 16.5 cents per dollar. The instinct is understandable: standing on 17 against a 10 loses more often than it wins. But a hit busts on any card from 5 up, and you turn a hand that sometimes wins into one that rarely does.

Splitting 10s against a weak dealer card feels clever because the dealer is likely to bust. The trouble is that a 20 already wins about 70 cents per dollar against a 6. Two hands starting at 10 average less, and the split costs 12.8 cents per dollar on the original bet.

Soft 18 against a 9

Standing on ace-7 against a dealer 9 is one of the most common errors among otherwise solid players, and it costs 8.2 cents per dollar. Eighteen looks like a made hand, but against a 9 the dealer finishes on 19 often enough that 18 is a loser. Because the hand is soft, a hit cannot bust it, so hitting is a free attempt to improve.

The small ones still add up

Some mistakes cost only a few cents: hitting 12 against a 6 (1.7c), standing on 12 against a 2 (3.9c) or not doubling 10 against a 9 (2.8c). Individually they are close calls, which is why players get them wrong. But the stiff hands from 12 to 16 are dealt in more than a third of all rounds, so a habit of misplaying them is paid for constantly.

Insurance

When the dealer shows an ace you are offered insurance, a side bet paying 2 to 1 if the dealer has blackjack. The dealer's hole card is a ten-value card about 30.8 percent of the time. To break even at 2 to 1 it would need to be one third, 33.3 percent. The gap means insurance returns -7.7 cents on every dollar you put on it, which is worse than almost any hand you will play. Our insurance page covers even money, which is the same bet in disguise.

Putting it in money

Take a player betting $25 who stands on soft 18 against a 9. Each time it happens they give up about $2.05 on average. Someone who never doubles 11 gives up about $8.35 each time they hold 11 against a 6. Over a few hundred hands these habits typically cost more than the entire house edge of a well played game, which is the whole case for learning the chart.

The stiff hands, every upcard

Hard 12 through 16 is where most everyday errors happen, so here is every case in one grid. Each cell shows the correct play, H for hit or S for stand, and how many cents per dollar the wrong choice costs. A small number means a close call; a large one means the wrong play is expensive.

Two patterns stand out. Against a dealer 4, 5 or 6, standing is right on every stiff total and hitting costs real money, because those dealer cards bust so often. Against a 7 or higher, hitting is right on every stiff total, and standing on 16 against a 7 costs 6.1 cents per dollar, because the dealer rarely gives you the bust you are hoping for.

The closest calls sit on the boundary: hard 12 against a 2 or 3, and hard 16 against a 10. Those cost only a few cents either way. They are worth learning properly, but it is the large numbers in this grid that do the real damage.

Frequently asked questions

What is the single most expensive habit?

Refusing to double. Doubling 11 against a 6 is worth 33.4 cents per dollar over just hitting, and similar gains exist on most 10s and 11s. Players who never double give away more than any other group.

Is it a mistake to follow the "never bust" rule?

Yes, against strong dealer cards. Never hitting a stiff hand means standing on 12 against a 10, which loses 54.0 cents per dollar, compared with 38.1 cents for hitting. Standing only works when the dealer is likely to bust.

Do these costs change with the rules?

Only slightly. A few doubling and soft hand decisions shift when the dealer hits soft 17, but every mistake on this page is a mistake under all common rule sets.

How should I learn the correct plays?

Start with the stiff hands and the doubling hands, since they are the most frequent and the most costly. The strategy chart and guide groups them in that order.

How these numbers were made: every figure on this page is calculated, not quoted. Our blackjack engine works out the exact expected value of every hand for an infinite deck, which lands within about a tenth of a percent of a 6 to 8 deck shoe. It assumes the dealer checks for blackjack, one split per hand, and split aces receiving one card each.

A note on risk. Basic strategy reduces the house edge to roughly half a percent. It does not remove it. Nothing here is gambling advice or a prediction of results. If gambling has stopped being entertainment, the National Problem Gambling Helpline is 1-800-522-4700, or ncpgambling.org.