Every bet forces a decision, and every defender has a leak: fold too much, and a bettor who bluffs with any two cards shows an automatic profit. Minimum defence frequency (MDF) is the maths that closes that leak — the smallest share of your range you must continue with to make bluffing unprofitable, no matter what the bettor holds.

The formula

MDF comes straight from the bet size, expressed as a fraction of the pot — nothing about your hand or the board matters here:

MDF = pot / (pot + bet)