MDF Calculator (Minimum Defense Frequency)

The GTO concept that matters most when you should ignore it

Minimum defense frequency is the GTO answer to a specific question: how often do I need to defend my range against a bet so that my opponent cannot profit by bluffing with any two cards? The answer is a clean formula. Pot divided by pot plus bet. Half pot bet, you must defend two-thirds of your range. Pot-sized bet, defend half. Overbet, defend less.

This is beautiful theory and most of the time it does not apply to your actual game. MDF assumes your opponent could be bluffing with literally any hand. In practice, your opponent at NL10 on a Tuesday night is not bluffing optimally. They are bluffing with hands that "look like bluffs" to them — busted draws, missed overcards, the occasional spite bluff after losing the previous hand. Their bluffing range is small and predictable, which means you can fold more than MDF dictates and still profit.

The reverse is also true. Against a player who never bluffs, MDF says you should still defend 50% against a pot-sized river bet. Reality says you should fold almost everything because the bet means he has it. GTO and exploitative play diverge here, and at low and mid stakes, exploitative wins by a wide margin. MDF is the floor of how often you should defend in a balanced strategy. It is not the prescription for what to do against a specific opponent.

Where MDF actually matters is at high stakes against thinking opponents. When you are up against a player who studies, balances their ranges, and bluffs at frequencies close to optimal, you cannot just fold to bluffs because you "feel weak." If you defend less than MDF, they will exploit you by bluffing more. You become the player they target. At those stakes, knowing MDF is what keeps you from getting run over.

For most online players, MDF is more useful as a sanity check than as a prescription. After a session, look at the spots where you folded the river to a bet. Were you folding more than the MDF threshold? If yes, did the opponent show down hands that justified those folds, or were they bluffing more than you thought? Across enough hands, this exercise reveals whether you are a chronic over-folder. Most low-stakes players are. They feel weak when their hand cannot beat much, forget that the opponent's range includes air, and let go of bluff catchers that should be calls.

One last note: MDF and pot odds are related but different. Pot odds tells you the equity your specific hand needs to call profitably. MDF tells you the percentage of your range you need to defend to prevent profitable bluffs. You can have a hand with insufficient pot odds equity that you should still call because of MDF (your range needs to defend even if this specific hand is borderline). And you can have a hand with sufficient pot odds equity that is correct to fold because better hands in your range need to take the call instead.

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