MDF (Minimum Defense Frequency) is one of the first calculations to learn in GTO poker. From your opponent's bet size, you can estimate the floor for how often you must continue so their bluffs cannot become profitable.
MDF is a range-level guideline, not a mechanical rule that "falling below this number is always a mistake." Individual hands are judged with pot odds and equity.
This guide covers the formula, common sizing benchmarks, the link to pot odds, practical uses in c-bet defense and bluff-catching, and frequent misunderstandings. For the big picture, see What Is GTO in Poker?
What Is MDF?
MDF is the minimum frequency you should continue (call or raise) when facing a bet. "Defense" means any action other than fold.
Why does this number matter? If villain is betting only bluffs and you fold too often, those bluffs profit automatically. MDF marks the break-even line where villain's bluffs are EV-neutral.
Important: MDF is not an order to "defend X% of your range no matter what." It is a lower bound: at this sizing, if villain bets only bluffs, theory says you must continue roughly this often or you get exploited.
The MDF Formula
The formula is:
MDF = Pot ÷ (Pot + Bet size)
Use the pot before the bet and the opponent's bet amount. If you express bet size as a fraction of the pot (e.g. half-pot = 0.5), you can also write:
MDF = 1 ÷ (1 + bet-size ratio)
Example: pot is 100, villain bets 50 (half-pot)
- MDF = 100 ÷ (100 + 50) = 100 ÷ 150 ≈ 66.7%
Example: pot is 100, villain bets 100 (pot-sized)
- MDF = 100 ÷ (100 + 100) = 50%
Common Bet Sizes and MDF
Reference values for sizes you will see in real games:
| Bet size (pot ratio) | Example (pot 100) | MDF |
|---|---|---|
| 1/4 pot (0.25) | 100 ÷ 125 | ~80% |
| 1/3 pot (0.33) | 100 ÷ 133 | ~75% |
| 1/2 pot (0.5) | 100 ÷ 150 | ~67% |
| 2/3 pot (0.67) | 100 ÷ 167 | ~60% |
| Pot-sized (1.0) | 100 ÷ 200 | 50% |
| 2× pot (2.0)* | 100 ÷ 300 | ~33% |
*2× pot: A theoretical reference only. In practice this appears almost exclusively near all-in or unusual spots. Learning 1/3 pot through pot-sized is enough to start.
Memory tip: Smaller bets → higher MDF (defend more often). Larger bets → lower MDF. Half-pot ≈ 67%, pot-sized ≈ 50%—memorizing those two covers a lot of spots.
How MDF Relates to Pot Odds
MDF and pot odds are two sides of the same bet size—different viewpoints:
| Concept | Whose view | Question |
|---|---|---|
| Pot odds | You (caller) | "What equity do I need to call?" |
| MDF | Your defending range | "At this size, what is the minimum continue frequency so bluffs cannot profit?" |
Example: pot 100, villain bets 100 (pot-sized):
- Pot odds (caller): Call amount 100. Pot after you call = original pot 100 + villain's bet 100 + your call 100 = 300. Required equity = 100 ÷ 300 ≈ 33.3%
- MDF (defender): Pot before call 100 ÷ (100 + bet 100) = 50% (calculated before you call)
Pot odds answer whether one hand is worth a call. MDF answers how often your range should continue at the lower bound. Use pot odds for a bluff-catch middle pair; use MDF to check if your range folds too much.
Using MDF in Practice
1. Defending vs C-Bets
On the flop, MDF helps you ask: "Am I folding too much?" If villain c-bets one-third pot (MDF ~75%) and you fold 90%, their bluffs may be becoming too profitable.
Board texture still matters. Dry boards favor the aggressor's range; wet boards leave more draws in the caller's range. MDF is a frequency floor—which hands defend is a separate question. See c-bet basics.
2. Bluff-Catching
On the river, when you lose to value but beat bluffs, MDF helps reverse-engineer how much bluff density villain needs in their betting range.
Pot-sized (MDF 50%): theoretically villain breaks even if half their bets are bluffs. If your hand beats those bluffs and meets pot odds (~33% required equity), calling is viable on paper.
If villain's range has almost no bluffs and your hand's equity falls short of required equity, folding below MDF is correct.
3. Spotting Over-Folding (Aggressor's View)
MDF also helps on offense. If villain defends far below MDF, your bluffs gain EV. Example: they fold 50% vs your half-pot c-bet (MDF ~67%)—your bluffs may be over-performing.
Review fold rates in nlh.poker hand history and stats to spot these gaps (hand review guide).
When Folding Below MDF Is Fine
This is the most misunderstood point. MDF is a range floor—you do not need to defend every hand to hit it.
The right approach: if you are below MDF, choose which hands should defend—bluff catches, draws, middle pairs—not force-call trash to hit a number.
Example: River Bluff-Catch
Setup:
- Pot: 100
- Villain's river bet: 100 (pot-sized)
- Your hand: middle pair (often loses to value, beats bluffs)
Math:
- MDF = 100 ÷ 200 = 50% (range continue floor)
- Required equity to call = 100 ÷ 300 ≈ 33.3% (this hand)
If your middle pair wins >33% vs villain's full betting range, calling works on paper. Reading bluff frequency and line consistency is the hard part—but separate MDF (range) from pot odds (hand).
Calling with pure air because "MDF is 50%" is wrong. Fold hands without enough equity; let other hands carry your range defense.
Common Misconceptions
Summary
- MDF = Pot ÷ (Pot + Bet size)—lower bound on defense frequency that makes bluffs EV-neutral
- Start with half-pot (~67%) and pot-sized (50%)
- Pot odds = single-hand call; MDF = range defense floor
- Use for c-bet defense, bluff-catching, and spotting over-folds
- Fold below MDF when equity is short, villain has no bluffs, or multiway
MDF is not just numbers to memorize—it calibrates your sense of over-folding and over-calling. After playing on nlh.poker, review hand history and ask: "At this size, what % did I continue?" Then revisit What Is GTO in Poker? and pot odds.
