What Is Minimum Defense Frequency (MDF)?

Minimum defense frequency (MDF) is the share of your range you must continue with against a bet so that your opponent can't profit by bluffing any two cards. It's the defender's side of the balance equation.

The formula

MDF = pot / (pot + bet)

• Against a pot-sized bet: 1 / (1 + 1) = 50%. You must defend half your range.
• Against a half-pot bet: 1 / (1 + 0.5) = 67%. You must defend two-thirds.
• Against a quarter-pot bet: ~80%.

The bigger the bet, the less you have to defend (because the bluff risks more). The smaller the bet, the more you must defend (because cheap bluffs need to be called more often).

Why it works

If you fold more than MDF allows, your opponent can bluff any two cards profitably — every fold pays for their bluff. Defending at MDF makes pure bluffs break even, removing their automatic profit.

MDF is a default, not a law

MDF assumes your opponent is capable of bluffing enough to punish over-folding. Against opponents who under-bluff — who rarely have it when they bet big — you should fold more than MDF, because their bets are mostly value. MDF protects you against a balanced bettor; against an unbalanced one, deviate.

Practical use

You don't compute MDF live to the decimal. You use it as a sense of "I'm folding too much here against a player who bluffs" — a guard against the most common leak, over-folding to aggression.

Common mistakes

• Defending MDF rigidly against players who never bluff.
• Over-folding to big bets against players who bluff plenty.