Backdoor Draws in Poker: Small Odds, Real Equity
A backdoor draw needs both the turn and the river to complete: three cards of a suit after the flop, or a straight that needs two running cards. A backdoor flush comes in only 4.2% of the time, about the value of one out. On its own it almost never justifies continuing; its value shows up with overcards, and on the turn, where it frequently becomes a real draw.
Q♦J♦ on T♠ 7♠ 7♦: overcards and backdoors
UTG opens, you call in the big blind with Q♦J♦. The flop comes T♠ 7♠ 7♦ and UTG bets 33% of the pot. Fold, call or raise?
See the answer
The price. A 33% bet asks for 19.9% equity.
The hand. No pair and no direct draw, but two overcards, a flush backdoor and straight backdoors: Q♦J♦ has 29.9% against A♥T♥ and 29% against A♥K♣, well above the price, and the table below shows that 2.6 to 4.2 points of it come from the flush backdoor alone.
The decision. The author's answer is the call: overcards plus backdoor equity continue profitably in the big blind's defending range.
What the backdoors add
The same ranks with and without the diamond backdoor, against four hands, with the turn and river to come:
| Opponent | Q♦J♦ | Q♣J♥ (no flush backdoor) | Gain |
|---|---|---|---|
| 6♥6♣ | 42.9% | 40.3% | 2.6 |
| A♥T♥ | 29.9% | 26.6% | 3.3 |
| A♥K♣ | 29% | 24.8% | 4.2 |
| 9♠9♦ | 26.6% | 23% | 3.6 |
Both hands share the straight backdoors (A‑K, K‑9 or 9‑8 complete Q‑J‑T); the difference is essentially the flush backdoor. Against 9♠9♦ the gain is smaller than against A♥K♣ partly because the opponent holds one of your diamonds.
The odds of backdoor draws
For Q♦J♦ on T♠ 7♠ 7♦, out of the 1,081 possible turn and river combinations:
| Backdoor | Combinations that complete it | Chance |
|---|---|---|
| flush (two more diamonds) | 45 | 4.2% |
| straight (A‑K, K‑9 or 9‑8) | 48 | 4.4% |
| either one | 90 | 8.3% |
A single out with two cards to come is worth 4.3%, so each backdoor here is worth about one out, and the two together about two. Three combinations complete both at once (A♦K♦, K♦9♦, 9♦8♦), which is why the total is 90 and not 93.
Where backdoors really pay: the turn
The backdoor rarely completes, but it often turns into a direct draw. On T♠ 7♠ 7♦, 22 of the 47 turn cards give Q♦J♦ a flush draw or a straight draw: 46.8%, nearly one turn in two. Those turns are the ones on which you can semi-bluff or call a second bet with real outs, then count them like any draw.
That is also why backdoors help realize equity: a hand that can improve on the turn keeps playing, where a hand with no backdoor tends to give up.
Two common mistakes
- Counting a backdoor as full outs. A backdoor flush is not 9 outs, nor even 2: it is about one out, because it needs two cards in a row.
- Folding small bets with overcards and backdoors. Against a third-pot bet, the price is 19.9%; overcards with a flush backdoor are often above it, as in the table on this page.
Keep going
- One missing card in the middle of a straight: the gutshot straight draw.
- The same flop with every opponent hand: paired boards.
- From outs to percentages quickly: the rule of 2 and 4.
- Compare equity with the price: pot odds.
Sources
- Odds counted over the 1,081 turn and river combinations; equities enumerated over every turn and river.
- Definition: PokerNews, "Backdoor" (poker terms).