Minimum Defense Frequency (MDF) in Poker, Explained

Minimum defense frequency (MDF) is the share of your range that must continue against a bet so that the bettor cannot profit by bluffing with any two cards. The formula is pot before the bet ÷ (pot before the bet + bet). If the pot is 100 and the opponent bets 50, MDF is 100 ÷ 150 = 66.7%, which means you should call or raise with about two-thirds of your range and fold the rest.

MDF is a concept from game theory (GTO, or game theory optimal strategy), but it is easy to use at the table. This guide assumes no-limit hold’em, a single opponent, and decisions made with a range, meaning all the hands you could hold in the spot, instead of one hand. It explains the formula, how bet size changes it, a worked example, and the limits of the idea. MDF is a guide, not an order to call, and it never removes variance or guarantees a profit.

What Minimum Defense Frequency Means

MDF answers one question: how often must you defend so that a bluff cannot show an automatic profit? Suppose an opponent bets and you fold every time. They can bet any two cards and win the pot immediately, so bluffing becomes free. If you defend often enough, their bluffs lose money and they must bet with real hands.

The key term is defend, which means continue with a call or a raise. Folding is the only action that does not defend. MDF does not tell you which hands to defend with or whether to call or raise, only how large the defending part of your range should be. Choosing the hands is a separate decision that depends on equity, blockers, board texture and position.

MDF is closely linked to bluff break-even frequency, the share of the time a bluff must work to show zero profit. The two always add up to 100%: if a bluff needs to work 33.3% of the time, you must defend 66.7%. For the bigger picture behind these ideas, see what GTO means in poker.

How the Formula Works and How Bet Size Changes It

Bigger bets give you more reason to fold, and MDF reflects this. A larger bet risks more to win the same pot, so the bettor needs the bluff to work more often to break even, and you can fold more without being exploited. The formula divides the pot before the bet by the pot plus the bet. Express the bet as a fraction of the pot: the MDF is 1 ÷ (1 + fraction). The bluff break-even is the bet ÷ (pot + bet), and the equity needed to call is the call ÷ (pot + bet + call).

The table below gives all three numbers for common bet sizes. Pot odds and MDF measure different things: pot odds tell you what equity a single hand needs to call profitably, and MDF tells you how much of your whole range should continue.

Read one row to see the logic. A pot-sized bet gives the bettor 50% bluff break-even: they risk 100 to win 100, so a bluff must work half the time. You therefore need to defend half your range. The one-third pot row is different: a bluff only needs to work 25% of the time, so you must defend 75% of your range, which is why small bets are hard to fold against. All values are rounded to one decimal place.

Example: Defending the Big Blind on a King-High Flop

Suppose a 100bb six-max cash game, the button opens to 2.5 bb and you call from the big blind. The pot is 2.5 + 2.5 + 0.5 = 5.5 bb. The flop is K♠ 7♦ 2♣, you check and the button bets half the pot, 2.75 bb. MDF is 5.5 ÷ (5.5 + 2.75) = 66.7%.

If your checking range holds about 90 hand combinations, you should continue with about 60 of them and fold about 30. Hands such as 9♥ 7♥ (middle pair) and strong draws are natural continues, while a hand like J♥ 5♦ with no pair and no draw is a natural fold. MDF sets the size of the defending group but not its contents, so the choice of hands still depends on equity and how the hand plays on later streets.

Now change the bet size. If the button bets the full pot, 5.5 bb, MDF falls to 5.5 ÷ 11 = 50%, so you continue with about 45 of the 90 hand combinations and fold about 45. A bigger bet lets you fold more because the bettor needs the bluff to work half the time. The same hand, 9♥ 7♥, is a comfortable call against the half-pot bet but a closer decision against the pot-sized one, since it needs more equity to call and many strong hands in the bettor’s range beat it.

The numbers assume the opponent is bluffing at a balanced rate. Against a player who rarely bluffs on this texture, folding more than MDF is correct; against one who bets every flop, defending more is correct. That is the central caution: MDF is a baseline for an unknown opponent, not a rule for a known one.

Common MDF Mistakes

Treating MDF as a rule to call is the first mistake. If the opponent’s range contains few bluffs, defending at MDF just pays off value bets. The formula assumes bluffs exist at a balanced rate, which is not always true.

Confusing MDF with pot odds is the second. A hand with 25% equity may meet the price to call a half-pot bet, but whether it belongs in your defending range depends on the rest of your range too.

Ignoring raises is the third. Raising is also a way to defend, so a range can defend at MDF with a mix of calls and raises. Finally, forgetting multiway pots: MDF is built for two players, and with more opponents each one’s range is stronger, so folding more often is usually correct.

How to Use MDF in Real Games

Use MDF as a sanity check on how often you fold. If a player bets half pot on every flop and you fold well over a third of your range, you are probably overfolding and giving up equity. Compare how often you fold with the table above. If you never fold, you are probably paying off value bets.

Adjust to the opponent. Fold more against bettors who show strength, such as a passive player who suddenly bets large on the turn, and defend more against aggressive players whose bluffing frequency is high. Board texture matters too: on boards where the bettor’s range is much stronger than yours, many solver-based approaches suggest folding more than MDF, because your hands do not realize their equity well. Real ranges are rarely exact, so treat any figure as approximate.

Finally, remember that MDF applies to every street, but the effect compounds: defending the flop, turn and river at MDF each time means calling many hands multiple times. Position, hand strength and the number of streets left all influence which hands continue. Variance means a correct defense can still lose, so judge decisions by the reasoning behind them. For the sizing side of the same ideas, see poker bet sizing after the flop.

Where to Go Next

MDF becomes more useful once you can describe ranges. Read about range shapes in polarized vs. linear ranges, which explains why bettors choose different sizes. For a concrete spot where defense frequency matters, see facing a river overbet with top pair, and for the preflop foundation of the big blind range see defending the big blind.