MDF (Minimum Defense Frequency) in Poker | How Often to Defend

Understanding MDF (Minimum Defense Frequency)

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🎯 MDF Is the "Floor for Not Folding Too Much"

If you defend less often than MDF, your opponent can profit by bluffing with any hand. In simple terms, MDF is the upper limit on how often you're allowed to fold.

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📐 The MDF Formula

MDF = Pot ÷ (Pot + Bet Size)

If the pot is 100 chips and your opponent bets 50 chips (half pot):

MDF = 100 ÷ (100 + 50) = 100 ÷ 150 ≒ 67%

This means if you don't defend at least 67% of the time by calling or raising, your opponent can profit from bluffing.

The Relationship Between α and MDF

Alpha and MDF are two sides of the same coin.

	Formula	Perspective
α	Bet ÷ (Bet + Pot)	Bluffer's view (how often must they fold?)
MDF	Pot ÷ (Pot + Bet)	Defender's view (how often must I defend to deny profitable bluffs?)

α + MDF = 100% — this always holds.

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📊 MDF by Bet Size

Here is MDF alongside α for common bet sizes.

Bet Size	α (Fold Threshold)	MDF (Defense Frequency)
1/3 pot	25%	75% (defend 3 out of 4 times)
1/2 pot	33%	67% (defend 2 out of 3 times)
2/3 pot	40%	60% (defend 3 out of 5 times)
3/4 pot	43%	57% (just under 3 out of 5)
Pot-sized	50%	50% (defend 1 out of 2 times)
2x pot	67%	33% (defend 1 out of 3 times)

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🃏 Worked Examples

What Happens When You Fold Too Much Against Small Bets

Pot: 300 chips. Opponent bets 100 chips (1/3 pot).

MDF = 300 ÷ (300 + 100) = 300 ÷ 400 = 75%

What if you fold 80% of the time (only defending 20%)?

• Opponent's bluff α = 25% (they only need 1-in-4 folds to profit)
• Your fold rate is 80% (far exceeds the 25% α threshold)
• Your opponent can profit by bluffing with any hand

In short, folding too much against small bets lets your opponent profit by bluffing with anything.

Folding More Against Big Bets Is Fine

Pot: 300 chips. Opponent bets pot-sized (300 chips).

MDF = 300 ÷ (300 + 300) = 300 ÷ 600 = 50%

Here, folding half the time is perfectly fine. Against big bets, the correct defense is to only continue with your strongest hands.

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🔑 MDF Means "Defend the Top, Fold the Bottom" of Your Range

The most important thing to understand about MDF is that it applies to your entire range, not to individual hands. Instead of "call MDF% of the time with this hand," think: line up your range from strongest to weakest, defend the top portion, and fold the bottom — MDF tells you where to draw the line.

Think in Terms of Your Range

For example, if your opponent bets half pot (MDF = 67%) and you have 10 different hands in your range:

1. Consider your full range
2. Select the weakest hands to fold (bottom 33% ≒ 3 hands)
3. Defend with the remaining top 67% (≒ 7 hands) by calling or raising

When choosing which hands to fold, don't just go by current equity alone. Also consider the potential to overtake your opponent's strong hands on later streets (draws and backdoor draws).

In other words, pick the weakest hands in your range to fold, and defend with the rest — that's the core idea behind MDF.

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💡 You Don't Need to Follow MDF Strictly in Practice

We've covered the MDF formula, but here's the most important point: MDF is a concept worth knowing, but you don't need to follow it strictly in practice.

MDF's Assumptions Don't Match Reality

MDF is calculated under the assumption that bluffs have 0% equity — that a bluff always loses when called. That's an extreme scenario.

In real poker, bluffs on the flop and turn typically have 10–20% equity. For example, backdoor draws or overcards give bluffs a chance to improve on later streets even when called.

Because of this gap, defending exactly at MDF often means you're defending too wide.

The Gap Between Solver Strategy and MDF

When we look at optimal strategies from solvers like GTO Wizard, actual defense frequencies deviate from MDF.

Situation	Solver Tendency
Facing a c-bet OOP (out of position)	Folds more than MDF suggests
Facing a bet IP (in position)	Defends close to MDF

The reason it's optimal to fold more than MDF when OOP is that the bluffer's hands have equity they can realize by checking back. Since bluffs aren't "guaranteed losers when called," the defender doesn't need to defend as wide as MDF suggests.

So how much should you actually fold? Here are rough guidelines:

Bet Size	MDF Fold Threshold	Solver Fold Frequency (approx.)
33% pot	25%	30–35%
50% pot	33%	35–40%
75% pot	43%	45–50%
125% pot	56%	55–60%

Compared to MDF, the actual fold frequency is about 5–10% higher across all sizes. This is the gap between MDF and practice.

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🎓 Practice Problems

Q1: Pot is 400 chips. Opponent bets 200 chips (1/2 pot). What is the MDF?

Show Answer

MDF = 400 ÷ (400 + 200) = 400 ÷ 600 ≒ 67%. The theoretical guideline is to defend about 2 out of 3 times. However, when OOP you can fold a bit more than this.

Q2: Same situation (pot 400 chips, opponent bets 200 chips at 1/2 pot). You're holding a marginal hand that could go either way — call or fold. Over 10 occurrences of this hand, you've folded 8 times. Is this a problem?

Show Answer

Yes, it's a problem. MDF for a 1/2 pot bet is 67%, but your fold rate is 80% (defense rate: 20%). If you're folding this much with marginal hands, your overall range defense frequency drops well below MDF, letting your opponent profit by bluffing with anything. Note: if you're holding a hand you should clearly fold (near-zero equity), folding 10 out of 10 times is fine. MDF is a range-wide frequency, not something applied to individual hands.

Q3: Your opponent bets 75% pot. MDF says the fold threshold is 43%. How much can you actually fold in practice?

Show Answer

The practical fold frequency guideline is about 45–50%. Folding a bit more than MDF's 43% is fine. Here's the summary for different bet sizes:

Bet Size	MDF Fold Threshold	Actual Fold Frequency (approx.)
33% pot	25%	30–35%
50% pot	33%	35–40%
75% pot	43%	45–50%
125% pot	56%	55–60%

Across all sizes, the actual fold frequency is about 5–10% higher than MDF.

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⚠️ Common Misconceptions

❌ "MDF is a number you must hit with every hand"

MDF is a frequency for your entire range. "If you face a half-pot bet, defend 67% of your hands" — it doesn't mean "call 67% of the time with this specific hand." Defend with the stronger hands in your range, fold the weaker ones — the result should be close to MDF overall.

❌ "Following MDF exactly means you're fine"

MDF is derived from a simplified model that assumes bluffs have 0% equity. In real poker, bluffs do have equity, and some hands in your range have near-zero equity (pure trash). Because of this, solver strategies deviate from MDF by a few percent. The right approach is to treat MDF not as an "absolute rule" but as a rough guideline.

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🎯 Summary

For a deep dive into the theory behind MDF, check out this article:

修正MDFとflopのdefense頻度に関する理論

An advanced theory article examining MDF critiques through model calculations and introducing corrected MDF

📖 65 min ★★★★★

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Now that you understand α (the bluffer's break-even point) and MDF (the defender's guideline), let's move on to the most fundamental concept in poker decision-making — Expected Value (EV). You'll learn what it means to "keep making correct decisions" in terms of numbers.