Minimum Defense Frequency: How Much of Your Range to Defend
Minimum defense frequency (MDF) is the share of your range you must continue with against a bet so that your opponent cannot profit by bluffing with any two cards. It equals pot ÷ (pot + bet), with the pot measured before the bet: against a bet of 50 into 100, defend 100 ÷ 150, so two thirds of your range. Defend less, and every bluff shows an automatic profit.
A bluff‑catcher on the river
Heads-up in a 3‑bet pot, you hold 9♣9♠ in the big blind. You check-called the flop K♠ 7♦ 5♥ and the turn 2♣; the river 2♠ pairs the board and the small blind moves all‑in for the size of the pot. Fold or call?
See the answer
How much to defend. The all‑in is the size of the pot, so MDF says to keep 50% of your range: half of the hands you reach the river with must call.
Where 99 sits. The all‑in is polarized: the straight draws that missed (6‑4, 4‑3, 8‑6) can only win by betting, and 99 beats all of them. Among your bluff‑catchers, it is one of the hands that should call.
The decision. Calling is the expected answer. Folding 99 here would likely leave you defending below MDF and let every missed draw jam at a profit.
MDF and required equity for each bet size
| Opponent's bet | MDF (share to defend) | Equity to call one hand |
|---|---|---|
| a third of the pot | 75% | 20% |
| half the pot | 66.7% | 25% |
| three quarters of the pot | 57.1% | 30% |
| the size of the pot | 50% | 33.3% |
| twice the pot | 33.3% | 40% |
The two columns answer different questions. The equity column is the pot odds of a single call; MDF is about your whole range: how many of your hands must continue so that a bluff does not win by default. Its mirror image, how often a bluff must succeed to break even, is explained in how often a bluff must work.
How to use MDF in practice
- Rank your range from strongest to weakest for this board.
- Keep the top MDF share: against a half-pot bet, roughly the best two thirds; fold the rest.
- Check the borderline hands with pot odds: a hand that has the equity to call stays in even near the bottom of the defended part.
When to defend less, or more
MDF is a protection against an opponent who could be bluffing with anything. Real opponents are not: against a player who almost never bluffs on the river, fold more than MDF says; against one who bluffs too much, defend more. MDF is the starting point when you know nothing, not a rule to follow against everyone.
Keep going
- Practice the equity side: the pot odds quiz.
- More river decisions like this one: what would you do.
- Big blind defense in practice: the 6‑max cash game trainer.
- One spot every day: the daily poker puzzle.
- What a decision is worth on average: expected value in poker.
- Why to bet small on a dry flop: c‑bet on dry boards.
- When several players called: c‑bet in multiway pots.
- Raising the bettor instead of calling: the check‑raise.
- Betting the turn again after a called c‑bet: the double barrel.
- Calling a river bet with a medium hand: the river bluff catcher.
- What a paired flop really changes: paired board strategy.
- When the bet is bigger than the pot: the overbet.
- Playing one opponent at a time: heads-up poker strategy.
- Which hands a big blind can still call with: the worst poker hands.
- What a defending medium hand beats: polarized vs merged range.
- Where this frequency comes from: GTO poker.
- Adapting to an opponent instead of a fixed frequency: exploitative poker.
- How many bluffs a river betting range holds for each size: the bluff to value ratio.
- One pair below the top: second pair, a hand to check and call.
For the rest of the hand from the big blind, see playing the big blind postflop.
Sources
- Every percentage on this page is computed from the formulas pot ÷ (pot + bet) and bet ÷ (pot + 2 × bet), checked on October 10, 2026.
- The answer to the spot follows rules written by the app's author; it does not come from a solver.