Part III: Business & Regulation · Gambling Mathematics & Probability

42. Minimum Defense Frequency (MDF)

Poker Math

Minimum Defense Frequency is the minimum percentage of a player’s range that they must continue with (by calling or raising) when facing a bet to prevent opponents from profitably bluffing with any two cards. MDF is a core GTO concept calculated as: MDF = Pot / (Pot + Bet). For example, facing a half-pot bet, MDF = 100 / (100 + 50) = 66.7%, meaning the player must defend at least two-thirds of their range. If a player folds more than the MDF allows, their opponent could profitably bluff every hand. MDF provides a baseline defense frequency when no specific opponent reads are available. Surveillance personnel in poker rooms should understand that players defending at GTO frequencies are typically well-studied, serious players.

In practice

MDF is a simplified model that applies most accurately on the river. On earlier streets, GTO solvers typically defend slightly less than MDF because the betting player has additional equity realization advantages. In practice, most players deviate from MDF based on opponent tendencies — folding more against tight players and defending more against loose players.

One entry from the Casino Industry Glossary — 1,157 terms written for surveillance, compliance and operations professionals rather than for players. Definitions describe industry usage; where a term carries a regulatory meaning, verify against the instrument that governs your jurisdiction.