MDF Calculator (Minimum Defense Frequency)

MDF calculator quick answer

Minimum defense frequency, or MDF, is the share of your range that must call or raise against a bet so a zero-equity bluff cannot profit automatically. MDF equals pot / (pot + bet). Against a half-pot bet, defend 66.7%; against a pot-sized bet, defend 50%.

• MDF formula for facing a bet: pot before the bet divided by pot plus bet.
• 33% pot bet: defend about 75% of your range and fold about 25%.
• 50% pot bet: defend about 66.7% of your range and fold about 33.3%.
• With 100 starting combos against a half-pot bet, defend at least 67 and fold no more than 33.
• Alpha is the fold rate a zero-equity bluff needs to break even; it is not the bettor's bluff frequency.

How to use MDF without following it blindly

MDF answers a narrow question: how much of your range must continue against a bet to stop a zero-equity bluff from making an automatic profit? If the pot is $100 before the bet and the opponent bets $50, MDF is 100 divided by 150, or 66.7%. A pot-sized bet produces 50% MDF. A larger overbet lets the defender fold more often because the bluff is risking more to win the same starting pot.

The percentage becomes more useful when you turn it into combinations. Suppose 100 combos reach the decision against that half-pot bet. Defending exactly 66.7 combos is impossible, so round up and continue with at least 67. Calls and raises both count. The calculator does that conversion for any range size up to the 1,326 possible preflop Hold'em combinations.

Alpha is often explained badly. It is not the opponent's allowed bluff frequency. Alpha is the fold rate a zero-equity bluff needs to break even: bet divided by pot plus bet. In the $50-into-$100 example, alpha is 33.3% and MDF is 66.7%. If the defender folds more than 33.3%, a bluff with no showdown equity earns money before rake.

The simple formula has limits. It assumes you are facing a bet, not a raise with a different risk-to-reward ratio. It also ignores range asymmetry, blockers, future betting, equity realization, and rake. Those details matter on every street, especially before the river. Use MDF to set a range-level checkpoint, then choose the actual calls and raises from the hands that perform best.

Exploitative play can move away from the checkpoint. If a sample shows that an opponent rarely bluffs a specific river line, folding more than MDF can save money. If an opponent attacks every sign of weakness, chronic over-folding gives those bluffs room to work. The point is to know the balanced reference before deciding that the evidence supports an adjustment.

Pot odds answer a different question. They tell you how much equity one hand needs to call. MDF tells you how much of the whole range should continue. A range can meet MDF by calling and raising its strongest candidates while folding hands that do not realize enough equity, even when the final defense count matches the calculator.