AA vs 55 Preflop All-in Strategy and Equity Analysis (100BB Deep)

I. Definitions and Background

In Texas Hold'em, AA (pocket aces) is the strongest starting hand, with preflop equity far exceeding other hand types; 55 (pocket fives) is a small pair, with low preflop equity when directly facing high cards, but high implied odds. 100BB (big blinds) effective stacks are common in cash games and tournaments, where preflop decisions must balance direct pot odds and postflop potential.

II. Equity and Mathematics

1. Preflop Equity

According to standard poker probabilities, AA vs 55 preflop all-in has roughly 80% equity for AA vs 20% for 55 (exact numbers vary slightly by suit, but the difference is small). AA's equity comes mainly from its overpair advantage, while 55 can only flip the script by hitting a set, with about a 12% chance of flopping a set plus subsequent draws (~8%).

2. Implied Odds

When effective stacks are deep (e.g., 100BB), small pairs like 55 prefer to see a flop because once they hit a set, they can often win the opponent's remaining stack. When calculating implied odds, factor in potential winnings. For example: facing an opponent's raise, calling with 55 costs 3BB; if you flop a set and the opponent holds an overpair (like AA), you can typically build a large pot, making the implied odds high enough.

III. Preflop Strategy

1. Strategy When Holding AA

• Standard Play: Usually raise (3-4BB) or 3-bet (9-12BB) to build the pot and isolate opponents. At 100BB depth, slow-playing AA is not recommended because postflop boards can give opponents reverse implied odds (e.g., AA being outdrawn by a straight or flush).
• Facing a Call from a Small Pair (55): If the opponent calls preflop, AA should continuation bet to force them to pay for chasing a set.

2. Strategy When Holding 55

• Preflop Call: Facing a raise (e.g., 3BB), 55 can usually call, provided effective stacks are deep enough (roughly 20:1 implied odds or better). 100BB fully satisfies this condition.
• Facing a 3-bet: If the opponent 3-bets to 9-12BB, the math on calling with 55 requires calculation: calling costs about 9BB, and you need to flop a set and win at least 90BB to be profitable. Therefore, unless the opponent's 3-betting range is very wide or they are likely to pay off postflop, folding is better.
• 4-bet All-in: Rarely, 55 might be used as a bluff or semi-bluff 4-bet, but this is extremely high risk.

IV. Practical Examples

Scenario 1: Button vs Big Blind, Effective Stacks 100BB

Button standard raises to 3BB, big blind holds 55.

• Analysis: Big blind calls 3BB, pot becomes 6.5BB. Probability of flopping a set is roughly 1/8, but if you hit, the chance the opponent has AA is very low; however, if they have an overpair, you can extract value. In the long run, calling is +EV.

Scenario 2: Small Blind vs Big Blind, SB has AA, BB has 55, Preflop All-in

SB raises, BB shoves all-in.

• Analysis: AA must call, with 80% equity. Expected value: 80% × 100BB - 20% × 100BB = +60BB (ignoring dead money).

V. Common Mistakes

Mistake 1: Believing small pairs (55) must always fold preflop

Correct: In deep stacks, calling a small raise with a small pair is +EV, especially when the opponent's range is strong and they are likely to pay off postflop.

Mistake 2: Believing AA can be slow-played to trap opponents

Slow-playing AA can lead to multi-way pots, increasing the risk of being outdrawn. At 100BB depth, fast play is usually superior.

Mistake 3: Ignoring implied odds and only looking at equity

Although AA has high equity vs 55, if 55 flops a set, AA can lose a large pot. Therefore, AA should make opponents pay a high price preflop.

VI. Summary

• In a preflop confrontation, AA is the clear equity favorite, but 55 has good calling value in deep stacks.
• At 100BB effective stacks, 55 should cautiously enter raised pots, relying mainly on implied odds for profit; AA should raise aggressively to protect its hand value.
• Final decisions must factor in opponent tendencies, postflop skill, pot odds, and other variables; do not rely on mechanical play.