Spanish 21 odds and dealer bust rates
Take the tens out of the deck and the dealer stops busting. That single fact explains most of what is different about Spanish 21 strategy.
Short answer
In a six-deck Spanish shoe the dealer busts less often than in blackjack with every weak upcard. Against a 6 the dealer busts 38.36% of the time rather than 42.28% EXACT. Against a 5 it is 37.93% instead of 41.84%. That is why you hit stiff totals in spots where blackjack tells you to stand: the dealer is less likely to do the work for you, and you are less likely to bust on the draw.
Dealer bust probability by upcard
All three columns are exact computations for six decks, conditioned on the dealer not already having blackjack, which is the situation you actually face once the peek is done.
| Dealer upcard | Spanish deck, stands soft 17 | Spanish deck, hits soft 17 | Standard deck, stands soft 17 |
|---|---|---|---|
| 2 | 31.72% | 32.06% | 35.52% |
| 3 | 33.67% | 33.96% | 37.57% |
| 4 | 35.79% | 36.10% | 39.73% |
| 5 | 37.93% | 37.93% | 41.84% |
| 6 | 38.36% | 40.14% | 42.28% |
| 7 | 26.57% | 26.57% | 26.19% |
| 8 | 24.58% | 24.58% | 24.37% |
| 9 | 23.00% | 23.00% | 22.92% |
| 10 | 23.12% | 23.12% | 23.02% |
| A | 17.26% | 20.24% | 19.91% |
Computed by exact enumeration of the dealer's draw from the remaining shoe. EXACT
Note the ace column. The Spanish dealer showing an ace busts 17.26% of the time when standing on soft 17 and 20.24% when hitting it. The dealer hitting soft 17 is the only rule that makes the dealer bust more, and it still costs you money, because the dealer also improves more often than the dealer busts.
Your own 21s are rarer too
A two-card 21 arrives on 4.181% of Spanish 21 hands, against 4.749% with a standard deck EXACT. That is a 12% reduction in the frequency of the best hand in the game, and it is a large part of what the bonuses are paying you back for.
How often each outcome happens
Measured over 100,000,000 simulated rounds of correct play, six decks, dealer stands on soft 17. SIM
| Event | Share of rounds |
|---|---|
| Player two-card 21 | 4.18% |
| Dealer blackjack | 4.01% |
| Round involves a double | 12.36% |
| Round involves a split | 3.25% |
| Round involves a rescue | 1.40% |
| Five-card 21 | 0.275% |
| 6-7-8 in any suits | 0.257% |
| Six-card 21 | 0.037% |
| 7-7-7 in any suits | 0.025% |
| Seven-or-more-card 21 | 0.0055% |
The bonus 21s are rare individually and meaningful together. Removing all of them raises the house edge by about 0.33 percentage points, which is two thirds of the entire edge in the standard game.
Variance
The standard deviation of a Spanish 21 round is 1.165 units of the opening bet SIM, slightly above blackjack because of the doubling freedom and the bonus payouts. Average total money wagered per round is 1.142 units, since doubles and splits add to the opening bet.
[TODO: publish win / push / loss frequencies split out by final outcome, and rounds per hour by table speed, once those are measured through this engine.]
Common questions
Why does the dealer bust less with no tens?
A dealer holding a stiff total, say 14, busts by drawing an 8, 9 or ten-valued card. Take four tens out of every 52 cards and the pool of busting cards shrinks. The dealer draws to 17 more often instead.
If the dealer busts less, why is the game still playable?
Because the rules give the value back: player 21 always wins, doubling is unrestricted, rescue exists, and the bonus 21s pay. Together those are worth roughly 0.97 percentage points, which is more than the deck change takes. See the house edge page.
Does the ace column really drop to 17%?
Yes, and it is conditioned on the dealer not holding blackjack. Once the peek has cleared, a dealer ace is a strong hand that rarely needs to take a risky card.