What are the odds of hitting your flush draw?
With four cards of the same suit, you need just one more to make a flush. A standard flush draw has nine outs: nine unseen cards that complete it.
One card to come: about 1 in 5.
If you see both cards: about 1 in 3.
After missing the turn: about 1 in 5.
Count your nine outs
Suppose you hold the ace and queen of hearts, and the flop brings two more hearts:
Your hand
There are 13 hearts in the deck. You can see four, leaving 13 − 4 = 9 hearts that make your flush. An out is a card that improves your hand; it is not automatically a card that wins the pot.
Where the probabilities come from
On the flop, you know five cards: your two hole cards and the three board cards. That leaves 47 unseen cards. These calculations assume no other cards are known.
- Hit on the turn: 9 / 47 = 19.1%.
- Hit by the river: subtract the chance of missing twice: 1 − (38 / 47 × 37 / 46) = 35.0%.
- Hit on the river after a miss: you now know six cards, so 9 / 46 = 19.6%.
Unseen opponents' cards and burn cards remain part of the unknown pool. If additional cards are exposed, adjust both the remaining outs and the number of unseen cards.
The rule of 2 and 4
For a quick estimate, multiply your outs by 2 for one card, or by 4 for two cards. Nine outs gives roughly 18% on the next card or 36% over two cards. These are shortcuts; the exact figures above are slightly different.
Use the two-card figure only when you will see both the turn and river. A flop call may buy just the turn, with another bet waiting before the river. If you're all-in on the flop, both remaining cards will be dealt.
What about a backdoor flush draw?
With only three cards of your suit across your hand and the flop, you need that suit on both the turn and river. For example, A♥ Q♥ on 9♥ 4♠ 2♣ is a backdoor heart draw.
10 / 47 × 9 / 46 = 4.2%
That's about 1 in 24, assuming you see both cards. Once the turn misses your suit, you cannot complete that flush on the river.
Making a flush is different from winning
The percentages above measure completing your suit. A smaller flush can lose to a higher flush. On a paired board, an opponent may have or make a full house or four of a kind. With four suited cards on the board, your hole-card rank also matters; a flush on the board may be shared.
Pair outs or straight outs can improve your chance of winning, but don't simply add them without checking for overlap and whether they actually beat your opponent. Your chance of winning depends on their hand and the full board.
Using the odds when facing a bet
Compare the cost of calling with the pot you can win. If the pot is 100 chips and your opponent bets 50, you call 50 to contest a final pot of 200. You need 50 / 200 = 25% winning equity to break even, ignoring rake and future betting.
A nine-out draw's roughly 19% next-card completion chance is below that threshold. Its 35% two-card chance is above it, but applies only if both cards are included in that price. This comparison assumes completing your flush wins and missing loses; actual equity can differ. Future bets and possible extra winnings also affect the decision.
Remember: nine outs, about 19% on the next card, about 35% across two cards.