CO 25bb Open Jam

Overview

CO 25bb Open Jam is a push/fold strategy commonly employed in No-Limit Hold’em tournaments (and occasionally in cash games) when the effective stack size is around 25 big blinds (bb) and the action is on the cutoff (CO). The term combines the position (CO), the stack depth (25bb), and the action (open jam, meaning open-shove all-in). This move is a central part of short-stack play, where the player chooses to go all-in rather than raise a smaller amount, thus eliminating the possibility of further aggression and forcing opponents to decide on a call or fold.

Strategic Rationale

At 25bb, standard opening raises (e.g., 2-2.5x) leave the player with a stack that is too shallow for comfortable postflop play. If the player raises small and gets called, the pot becomes a significant portion of their remaining stack, often committing them on most flops. By open-jamming, the CO player simplifies the decision tree and applies maximum pressure on the blinds and other players yet to act. The jam leverages fold equity (the chance that opponents fold) and ensures that when called, the hand’s equity is realized immediately without postflop mistakes.

ICM Considerations

In tournaments, the Independent Chip Model (ICM) heavily influences this decision. With 25bb in the CO, open-jamming is often correct against tight opponents, especially on bubble or near pay jumps. However, against loose callers or when the stack is too large (above 30bb), open-jamming can be wasteful because it risks elimination with little additional fold equity. The 25bb threshold is considered a “sweet spot” for open-jamming from late positions, as it is small enough to maintain fold equity yet large enough to damage opponents’ stacks.

Hand Selection Ranges

A typical GTO-inspired range for a CO 25bb open jam might include: strong value hands (e.g., 77+, AJ+, KQ) to balance with some suited connectors (e.g., 65s, 87s) that play well against calling ranges. The exact range depends on opponent tendencies, ante size, and tournament stage. In practice, many players tighten their range in early positions and widen it in late positions, but the CO is considered a profitable spot for these shoves because only three players remain to act (BTN, SB, BB).

Risks and Adjustments

Open-jamming 25bb from the CO is not always optimal. If the blinds are very aggressive callers (e.g., calling with hands like A2s or K9o), the jam loses value. Similarly, if the effective stack of a caller is deeper, the shover risks being dominated. Skill differences also matter: a weaker player may prefer smaller raises to see flops, while a stronger player may embrace the simplicity of push/fold. Additionally, in cash games, the rake can affect profitability, making smaller raises preferable.

Related Concepts

• Push/Fold Strategy: The general approach of only shoving/folding when the stack is short (typically under 20bb). At 25bb, open-jamming is an extension, though some experts recommend a mixed strategy with smaller raises.
• Cutoff (CO) Position: The seat two to the right of the button, often seen as a late position with strong steal opportunities.
• Effective Stack Size: The smallest stack among the players in the hand, which determines viable actions. For a 25bb CO open jam, effective stack against a 25bb opponent is 25bb.
• ICM (Independent Chip Model): A model used to calculate tournament equity, influencing whether an open jam is profitable based on payout structure.

Conclusion

CO 25bb Open Jam is a powerful but situational play. It works best in tournaments with high antes and opponents who fold too much. Players should adjust based on table dynamics, stack distribution, and their own skill level. While simple to execute, mastering the decision of when to open-jam from the cutoff at 25bb requires a deep understanding of range construction, fold equity, and risk management.