Minimum Defense Frequency (MDF) in Poker

Instead of asking “should I call with this hand,” minimum defense frequency asks a harder question: how much of my entire range has to keep fighting so the person betting can’t just print money by bluffing? That reframing is the whole idea. MDF is the smallest fraction of your hands you must continue with — call or raise — to stop a bettor from profitably firing any two cards at you. And the math fits on one line: MDF = pot ÷ (pot + bet).

Where the formula comes from

The formula is the bettor’s bluff math turned inside out. Suppose they bet B into a pot of P. A pure bluff wins the pot when you fold and loses B when you call. For that bluff to break even, you have to fold often enough that the pot covers the times they get looked up — a fold rate of B ÷ (P + B).

Everything you don’t fold is what you defend:

MDF = 1 − [B ÷ (P + B)] = P ÷ (P + B)

Defend at least that share and a bluff of pure air breaks even at best. You’ve taken away the free money. Notice what MDF does not depend on: the specific cards, your equity, the runout. It’s a pure function of bet size, which is what makes it quick to use mid-hand.

Reading it off by bet size

Because MDF depends only on the bet-to-pot ratio, the common sizes are worth memorizing outright:

Bet size (fraction of pot)	MDF (defend at least)	You may fold up to
Quarter pot (0.25x)	80%	20%
Half pot (0.5x)	67%	33%
Two-thirds pot (0.67x)	60%	40%
Three-quarters pot (0.75x)	57%	43%
Full pot (1x)	50%	50%
Overbet (1.5x)	40%	60%
Overbet (2x)	33%	67%

The pattern is intuitive: the bigger the bet, the less you have to defend. A large bet risks more of the bettor’s own stack, so fewer bluffs are needed to threaten you, and you’re allowed to fold more. It’s exactly why overbets fold out so much of a range — and why bettors reach for them when they want to apply maximum pressure with a polarized holding.

Working a spot through

The pot is $80 and your opponent bets $40, a half-pot bet. MDF says:

80 ÷ (80 + 40) = 80 ÷ 120 ≈ 67%

Continue with about two-thirds of the range you’d have here, and you can release the worst third. Put numbers on it: if your river range is 15 combinations, MDF means keeping roughly 0.67 × 15 ≈ 10 combos and folding around 5. Fold 8 or 9 instead and the opponent can bet any two cards for profit — your extra folds are literally paying for their bluffs. Which hands you keep is a separate skill; pick the ones with the best equity and the most useful blockers. MDF only sets the count.

MDF and pot odds are not the same tool

They fall out of the same bet-to-pot ratio, so they get confused constantly, but they answer different questions:

• Pot odds — the price one hand is getting on a call. Use it to decide whether a specific draw or bluff-catcher is worth continuing.
• MDF — how much of your whole range must continue so bluffs don’t auto-profit. Use it to check you’re not over-folding into free profit for the bettor.

Pot odds is a single-hand question. MDF is range-wide discipline. You’ll often use both in the same decision: MDF to know you need roughly ten continuing combos, pot odds to sort out which marginal hand makes the tenth.

When to throw it out

Here’s the part most write-ups bury. MDF is a defensive baseline against a balanced bettor — someone bluffing the theoretically correct amount. Almost nobody at a live or low-stakes table actually does that. MDF stops a strong, balanced opponent from exploiting you; against everyone else, rigidly defending at MDF is itself the mistake.

Adjust like this:

• Against under-bluffers (most low-stakes players). Defend less than MDF. If their bets are nearly all value, you owe them nothing — fold your weak hands freely and stop paying off made hands.
• Against over-bluffers. Defend more than MDF, sometimes with your entire range, because every extra bluff you catch is pure profit.
• When the board is bad for bluff-catching. Raw MDF ignores whether your hands can even beat a bluff. If nothing in your range beats a value bet, over-folding is correct — the formula doesn’t know the texture, you do.

Why it costs more on the river

MDF applies on any street where you face a bet, but the price of getting it wrong climbs as the hand goes on. On the flop you usually hold draws and backdoor equity that make continuing cheap and easy, so reaching MDF is rarely a stretch. By the river every draw has hit or missed, and your continuing range is nothing but made hands — so over-folding rivers is where most players quietly bleed the most.

A workable rule of thumb: be strict about MDF on the river, looser earlier. Early streets let you defend with hands that can still improve; late, you’re deciding with hands that are already good or already dead. Talking yourself out of a river bluff-catcher you should have kept is one of the most expensive recurring leaks in the game, and it’s exactly the leak MDF exists to plug.

The habit to build

Face a bet, run pot ÷ (pot + bet) in your head, and continue with at least that fraction of your range — unless you have a specific read that the bettor doesn’t bluff enough to earn it. That’s the whole discipline. It won’t tell you which cards to keep, and it won’t beat a passive player who never bluffs, but it will keep a good opponent from turning your folds into free profit. For the wider picture of how theory and exploitation meet, the expected value and preflop and GTO hubs pick up where the formula stops.