I worked the pits in Vegas for thirty-eight years. I have seen every variant of blackjack come and go. Spanish 21 is the one that casinos love because it takes players who think they are playing blackjack and charges them a much higher fee for the privilege.
Both games have dealers and players.
First, the shared features. Both games deal from a shoe of multiple decks. Both games use 21 as the target. Both games have dealers and players. Both games pay blackjack (21 in two cards). The similarities are intentional; they make Spanish 21 look familiar to someone who has never played it before.
Here is where the difference starts. Spanish 21 uses a deck with all the tens removed. A regular deck has 52 cards. Spanish 21 uses 48-card decks. No 10s of any suit. Only J, Q, K. This changes the probability distribution. More face cards relative to number cards. The deck is closer to being composed entirely of high-value cards.
Second: the player busts on 22 and pushes instead of losing. In regular blackjack, if you go over 21, you lose immediately. In Spanish 21, if you go to exactly 22 (like 10-Jack-2 in a situation with three cards), you push (tie with the dealer). This sounds good; it is not. The removal of the tens already skews the deck toward high cards, which means more busting. The 22 push rule exists to make up for this, but it does not fully compensate.
Third: blackjack pays 3-to-2 in Spanish 21, same as regular blackjack. But wait, you need three cards to make 21 in Spanish 21 sometimes because there are no tens. You can make 9-10-2 if the casinos put tens back in. But they did not. So blackjacks in Spanish 21 are rarer and they still pay 3-to-2.
Fourth: the dealer must hit on 17 in Spanish 21, sometimes. Regular blackjack dealers hit on 16 or lower and stand on 17 or higher. Some Spanish 21 games have the dealer stand on all 17s, some have the dealer stand only on hard 17 (hitting on soft 17s). The variation alone makes Spanish 21 harder to play with basic strategy.
Fifth: Spanish 21 offers a "Late Surrender" option. You can give up half your bet after the dealer checks for blackjack. Regular blackjack sometimes offers this. Spanish 21 makes it standard and heavily advertised. The idea is that you can surrender weak hands and recover half your loss. The reality is that the deck composition and rule changes have made the game worse for you; the surrender option is a small compensation.
The house edge in Spanish 21 is approximately 0.40 percent when played with perfect basic strategy. The house edge in regular blackjack is 0.60 percent. This makes Spanish 21 sound better. It is not, because Spanish 21 basic strategy is different. New players who sit down at Spanish 21 and play regular blackjack basic strategy will face a house edge of 2-3 percent because they will make wrong decisions (hitting when they should stand, standing when they should hit, due to the deck composition changes).
The casinos market Spanish 21 as a better game. Technically, if you play perfectly, it is slightly better. Practically, because most players do not adjust their strategy to the deck composition, they lose more money at Spanish 21 than they would at regular blackjack.
Stay away from Spanish 21 unless you have studied the specific basic strategy for it. Regular blackjack, played with regular basic strategy, is a better game for the average player. The house has already taken enough; you do not need to give them the additional edge by playing a variant you do not fully understand.
