MDF (Minimum Defense Frequency)

What Is Minimum Defense Frequency?

Minimum Defense Frequency (MDF) is the minimum percentage of your range you must continue with, by calling or raising, to prevent an opponent from profiting with pure bluffs. If you fold more often than MDF allows, your opponent can bet any two cards and show an automatic profit, regardless of what they hold. MDF is the defender's half of the balance that keeps a betting range honest; the bettor's half is the bluff-to-value ratio set by pot odds.

The MDF Formula

MDF is calculated as:

MDF = Pot Size / (Pot Size + Bet Size)

It can also be expressed as MDF = 1 - alpha, where alpha is the break-even frequency for a pure bluff. The two are mirror images of the same relationship: if a pot-sized bluff needs a fold 50% of the time to break even, the defender must continue at least 50% of the time to deny it.

Common MDF Values to Memorise

The MDF Calculator computes exact values for any bet size. Note how quickly MDF falls as the bet grows: a small bet demands that you defend most of your range, while an overbet lets you fold two thirds of it.

MDF in Practice

MDF is a theoretical guideline for balanced play, not an absolute rule. Against an opponent who never bluffs, you should fold more than MDF suggests. Against a chronic over-bluffer, you should call wider. But MDF provides the default that prevents exploitation when you lack specific reads, and it is a fast way to spot your own leaks: if you fold to a half-pot bet more than a third of the time on a board where your range is not capped, you are giving away the pot.

Where MDF Breaks Down

MDF assumes the bettor's bluffs have no equity and that your range is strong enough to defend. Neither is true on the flop. A flop bluff with a flush draw will still win a third of the time when called, so the bettor can bluff more than alpha suggests, and a defender whose range is dominated by the board (a big blind facing a bet on A-K-7, for example) should fold far more than MDF. Solvers routinely have the out-of-position player folding 60% or more to a small flop bet on boards where MDF says 75% must continue. Treat MDF as the river baseline and as the ceiling for how much you can fold on earlier streets when the ranges are close.

MDF and Bluff Catching

MDF directly determines which hands become bluff-catching candidates. After ordering your range from strongest to weakest, you continue with the top MDF percentage and fold the rest. The hands at the boundary are your marginal bluff-catchers, the ones that are indifferent between calling and folding against a balanced betting range. Blockers move hands across that boundary: a hand that blocks your opponent's value combinations and unblocks their bluffs is a better call than its raw strength suggests.

Practical Example

The pot is $100 on the river and your opponent bets $50. MDF is 100 / 150 = 67%, so you need to continue with about two thirds of the hands you arrive at the river with. If you reached the river with 30 combinations, roughly 20 of them should call or raise. If only your top 12 combinations continue, your opponent can bluff every missed draw profitably, because you are folding 60% against a bet that only needs a fold one third of the time.

Learn More

MDF vs actual GTO defense shows, with solver data, where the formula and the equilibrium diverge. Bluff-catching is math, not instinct covers the river decision in depth. Postflop+ is the training ground: its GTO opponent bets at different sizes across board textures, so defending at the right frequency becomes automatic rather than calculated.