Minimum defense frequency (MDF) is the share of your range you need to continue with (call or raise) when facing a bet, so that your opponent cannot make an instant profit by bluffing with any two cards.
The MDF formula
MDF = pot ÷ (pot + bet)
The pot is measured before the bet. The rest, bet ÷ (pot + bet), is the break-even fold rate a pure bluff needs.
MDF by bet size
| Bet size | You must defend | A bluff needs folds |
|---|---|---|
| 25% pot | 80% | 20% |
| 33% pot | 75% | 25% |
| 50% pot | 67% | 33% |
| 75% pot | 57% | 43% |
| Pot | 50% | 50% |
| 2x pot | 33% | 67% |
An MDF example
The pot is $60 and your opponent bets $30 (half pot). MDF = 60 ÷ 90 = 67%. If you fold more than one-third of your range here, your opponent profits by betting every hand, including pure bluffs.
When to ignore MDF
MDF is a defense against a perfect, balanced opponent. Real players are not balanced. If a player rarely bluffs, fold far more than MDF suggests. If they bluff too much, call more. MDF also matters less when your range is weak because of earlier actions. Use it as a check on whether you are folding too much, not as a strict rule.
Compare MDF with the calling odds in the pot odds calculator. More terms in the poker glossary.