Minimum defence frequency (MDF)
Minimum defence frequency is the share of your range you must continue with against a bet so that a bluff with any two cards cannot automatically profit. It is calculated as pot divided by pot plus bet.
MDF = pot / (pot + bet)
Facing a bet, folding too often turns your opponent's whole range into a profitable bluff. MDF is the continuing share that removes that free profit: defend at least this fraction and a bluff with no equity breaks even at best.
Worked example. The pot is 100bb and your opponent bets 50bb:
MDF = 100 / (100 + 50) = 0.667
You must continue with about 67% of your range. Fold more than a third here and any two cards print money as a bluff.
MDF is a pressure test, not a target: it assumes the bluffs have zero equity and you are at the bottom of your range nowhere. Against real opponents who under-bluff, folding more than MDF suggests is often correct.
Try it live
The MDF calculator below is the same tool as the standalone page, running right here.
Pot before the bet, and the bet villain makes into it.