Backdoor

A runner-runner draw: you need the turn AND the river

Definition

A backdoor (runner-runner) draw needs two perfect cards — the turn AND the river. The textbook case is the backdoor flush: two cards of a suit in hand, only one on the flop; the flush arrives about 4.2% of the time. Backdoor straights are in the same ballpark depending on the layout. Taken alone, ~4% is worth nothing. The value of backdoors lies elsewhere: they're the equity crumbs that break ties in close decisions. Between two c-bet or float candidates, the one carrying a backdoor flush and a backdoor straight is clearly better — not for the 4%, but because many turn cards upgrade the hand into a real draw (9 flush outs, a gutshot) that lets you keep the aggression going with genuine equity. That's exactly why solvers pick their bluffs among hands with backdoors: they "catch" a favorable turn far more often than their raw equity suggests.