How Often You Double and Split, and What It Adds to Your Bet

Most of the time, blackjack is a one-unit game. You put a chip down, you hit or stand, the dealer plays out their hand, and the chip moves one way or the other. But basic strategy also tells you, on a minority of hands, to push more money out: to double, matching your bet for one more card, or to split a pair into separate hands that each carry their own bet.

Those plays are rare one at a time and heavy together. In our simulation, 10.27 percent of rounds include a double, 2.48 percent include a split, and 0.73 percent include both. Add everything up and the average round carries 1.1318 units of total wager, so a player betting one unit flat actually puts about 113 units across the table every 100 rounds.

Here is where that extra money goes, play by play and hand by hand. For which chart cells call for a double, see our guide to when to double down; for the pair decisions, splitting pairs covers every one.

The simulation

The numbers come from our simulation: about 62 million rounds, one player, a flat one-unit bet, basic strategy from the app's 4 to 8 deck chart. The rules: six decks, dealer stands on soft 17 and peeks, blackjack pays 3:2, double on any two cards, double after split, split to four hands, one card to split aces with no resplitting, no surrender, cut card at 75 percent penetration.

These are the same rounds behind our piece on what share of rounds you win, push and lose, rerun with more detail, and they reproduce that article's figures exactly. A round is one starting bet together with everything that grows out of it.

How often a double or a split arrives

Counting each round once, 12.02 percent of rounds (10.27 plus 2.48 minus 0.73) put more than the opening unit at stake.

Counted per 100 rounds, the plays total 10.40 doubles and 2.79 splits, both higher than the round shares, and the reason is mechanical: one round can contain the same play more than once. A split whose two hands both double is two doubles in one round, and a pair of 8s that resplits to four hands is three splits in one round. For scale, the player hit or doubled 66.4 times per 100 rounds: a round with a double comes about once every ten rounds, one with a split once every forty.

What actually lands on the table

The distribution of total wagers per round is steeply bottom heavy:

The rows above one unit add up to about 12.02 percent, matching the arithmetic above, and the whole table averages out to the 1.1318 units per round. The two-unit row is a single double or a plain split into two hands; three units can be two split hands with one of them doubled, or a split into three; the eight-unit row, vanishingly rare, is four split hands with every one of them doubled. The large majority of rounds never grow at all, yet the 12 percent that do lift the average wager more than 13 percent above the flat bet.

The dealer upcard view

The extra money is not spread evenly. It clusters hard against weak upcards:

Against a 5 or a 6, more than one round in five includes a double, and the average round carries about 27 percent more money than the starting bet. The doubling share climbs steadily from 9.85 against a 2 to 21.48 against a 5, then falls off a cliff against the strong upcards.

Against an ace the double column reads exactly zero. In a game where the dealer stands on soft 17, no cell in the 4 to 8 deck chart doubles against an ace; even hard 11, the best doubling hand in the game, hits instead, as our piece on doubling hard eleven explains. The 10 and ace rows also include the dealer's blackjacks, rounds that end with no one acting, which pulls those averages toward the one-unit baseline.

The starting hand view

Grouped by the hand you are holding, the same numbers look like this:

Every other starting hand sits at exactly 1.0000: non-pair hard 5 through 8 and 12 through 19, a pair of 10s, soft 19 and 20, and naturals. None of them ever doubles or splits.

The doubling percentages can be read straight off the chart. Hard 11 doubles against 2 through 10, which is 12 of the 13 upcard ranks, 92.3 percent, before the rounds lost to a dealer blackjack trim it to the observed 89.85. Hard 10 and 5,5 double against 2 through 9, 8 of 13 ranks or 61.5 percent, and land at 61.31 and 61.29. Hard 9, soft 17 and soft 18 double against 3 through 6, 4 of 13 ranks or 30.8 percent, and land at 30.53, 30.59 and 30.96.

For the hands that never split, the average wager is exactly one unit plus the doubling share, which is why hard 11 lands at 1.8985. Only pairs can pass two units, because every split hand carries its own bet and, with double after split, can double too. A pair of 8s puts the most money on the table of any starting hand, 2.38 units on average; a pair of aces comes next at 1.96. Our piece on what happens after a split follows those hands to the finish.

Why the extra units matter

The chart does not send extra money out at random. In the same simulation, doubled hands won 55.17 percent of the time, pushed 6.94 and lost 37.89, a far better record than rounds overall, which won 43.34, pushed 8.77 and lost 47.89.

This is the machinery behind a result that looks paradoxical. As our win share article explains, the player loses 4.55 points more often than they win, yet the average result is about -0.44 percent of the starting bet, because an average win is bigger than an average loss. The extra half unit on naturals and the extra units from doubles and splits win back about 4.1 of those 4.55 units per 100 rounds; doubles and splits alone recover 1.84 in that article's arithmetic. The three hands that double most, hard 11, hard 10 and 5,5, all rank among the ten most valuable in our table of what each starting hand is worth.

Two denominators, one loss

The average result above is -0.436 percent of the starting bet. Measured against all money wagered instead, it is 0.436 divided by 1.1318, a loss of 0.385 percent.

Both figures describe the same game with different denominators. One asks what a round costs against the single unit that opened it; the other asks what it costs against the roughly 1.13 units that actually crossed the table. Per 100 rounds the average loss is the same 0.436 units either way; only the base changes. When one figure looks too good next to another, check the denominators first, the habit our article on the house edge asks for when it separates the amount wagered from a buy-in.

These are long-run averages over tens of millions of rounds, not a description of any evening, and nothing here is advice on how much to wager. To check your own doubling decisions, 21 Trainer gives instant feedback with an explanation on every decision, and its charts redraw for the selected rules. The Pro upgrade adds a bankroll simulator with virtual chips.

Frequently asked questions

How often do you double down in blackjack?

In our simulation of about 62 million rounds of basic strategy, six decks with the dealer standing on soft 17, a round included a double 10.27 percent of the time, and 10.40 doubles landed per 100 rounds, since each hand created by a split can double. For scale, the player hit or doubled 66.4 times per 100 rounds.

How often do you split pairs in blackjack?

In 2.48 percent of rounds in our simulation, with 2.79 splits per 100 rounds, because one round can split more than once: a pair of 8s that splits and resplits to four hands is three splits in a single round. Rounds with a split are about a quarter as common as rounds with a double, so pair decisions come up far less often than doubling ones.

How much is wagered in the average blackjack round?

With doubles and splits included, 1.1318 units per round in our simulation, betting one unit flat. Nearly 88 percent of rounds never exceed the opening bet, 11.16 percent end at exactly two units, and the rest climb from there, for about 113 units per 100 rounds rather than the flat 100 the base bets suggest.

Why are there two percentages for the average blackjack loss?

Because the loss can be measured against two different amounts. In our simulation the average result is -0.436 percent of the starting bet, which works out to a loss of 0.385 percent of all money wagered once doubles and splits are counted: 0.436 divided by the 1.1318 units wagered per round. Same game, same loss, different denominator, so check which amount a figure is measured against before comparing.

Which blackjack hands put the most money on the table?

A pair of 8s, at 2.38 units on average in our simulation once the split, resplits and doubles after them are counted, the most of any starting hand. A pair of aces averages 1.96 units, and hard 11, which doubles in 89.85 percent of the rounds it appears in, averages 1.90. Non-pair hard 12 through 19, a pair of 10s, and soft 19 and 20 never go past one unit.

Keep reading

• When to Double Down in Blackjack
• Splitting Pairs: Always, Never, and It Depends
• What Share of Blackjack Rounds Do You Win, Push and Lose?