MDF is the minimum share of your range you must continue with against a bet so the bettor can’t profitably bluff any two cards. It equals pot ÷ (pot + bet).
MDF answers a different question than pot odds. Pot odds tell one hand whether to call; MDF tells your whole range how often it must defend to stay unexploitable. Defend less than the MDF and the opponent can bluff any two cards for an automatic profit.
Because MDF depends only on bet size, bigger bets lower it — a defender owes less against a large bet. In practice you meet the MDF with your best bluff-catchers and give up your worst hands, and against players who under-bluff you can correctly defend below the MDF (an exploitative over-fold).
Small bets demand more defense than big ones because they risk less: MDF is 75% against a one-third-pot bet, 67% against half pot and 50% against a pot-sized bet. The hands that fill that share are your strongest hands, your best draws and enough bluff-catchers; the bottom of your range still folds. The classic misuse is applying MDF to one hand — ‘MDF is 55%, so I call’. For a single hand the question is always its equity against the price; MDF only tells you how wide the whole continuing range must be. In multiway pots the defense is shared between the players left, so no single player owes the full MDF.
Worked example
FAQ
What is the MDF against a pot-sized bet?
Exactly 50%. MDF = pot ÷ (pot + bet), and when the bet equals the pot that’s pot ÷ 2·pot = 50%.
Should you always defend the full MDF?
No. MDF is the unexploitable baseline. Against opponents who rarely bluff you should over-fold; against players who bluff too much you should over-call beyond the MDF.