What can I do to calculate my odds in a hand?
If I have 2 cards of the same suit in the hole, and 2 board cards with those suits on the flop, what are the chances that I will hit my flush:
- On the turn?
- By the end of the hand?
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After the flop you've seen 4 cards of your suit, and 1 of another suit. This leaves 9 cards of your suit, and 38 of a different suit; your odds of completing your flush on the turn are thus
If the turn hasn't completed your flush, your odds of completing it on the river are
This means that the total odds for completing a flush - which should matter for example if you're going all in after the flop - are
(19.14%) + (19.5%*(1-19.14%)) = 34.96% (the odds of completing on the turn, plus the odds of completing on the river times the odds of not completing on the turn).
A good rule of thumb I always use for a flush draw is multiply outs(13 spades - 4 spades) with 4 on the flop and 2 on the turn. This ways it's much easier to remember and you aren't that far away from the correct percentage.
On the flop = number of flush outs x 4 = (13-4)x 4 = 36%
On the turn = number of flush outs x 2 = (13-4)x 2 = 18%
Obviously a "naked" flush draw is not a very good hand to move all-in with on the flop since you are most likely to be up against a much stronger hand if your opponent raises you. However, if you are holding a flush draw as well as two cards that are higher than the cards on the flop, this is a much stronger hand since you are drawing to a higher pair versus a potential top pair on the flop.
example: s = spade.
AsKs vs 88
flop: 4s 7h 2s
here you have 9 outs for the flush + 3 aces and 3 kings to hit against his pair of eights. This works out to a total of 9+3+3 = 15 outs => 15 x 4 = 60% .. although the correct answer is a bit smaller.. so 55% is more accurate.
My conclusion is that if you really "have to" move all-in with a flush draw, you should do it with two high cards of the same suit! :)
Here is a nice tool called pro poker tools.com to help you calculate your chances!