I've got a question about calculating poker odds.

I've been doing the x4 and x2 rule the entire time, and only recently, when going through some online material, found out that basicly, the x4 is counting 2 cards and the x2 counts one card. I feel dumb now....

This means that if, let say I have a flush draw on the flop, I do 9 x 4 and have 36% or 2:1, and on the turn, I do 9 x 2 and have 18% or 4:1.

Now on this page https://www.cardschat.com/f57/how-do...d-odds-243852/ , OP says your odds from flop to turn are 4:1 and from flop to river 2:1.
They say that you only use the rule of 4 when facing an allin on the flop, and not with future betting, because you (if the villain is unknown) don't know if you will need to call a second bet or not. This means that I've been doing the math entirely wrong this entire time? You need to do the rule of x2 on the flop and turn if facing unknown bets?

So how do I use this information in poker? Do I use the general % of 36 as a guideline for the entire 5 card hand and the 18% to use for the next card?
So if he bets 3$ pre, I'm the only one who calls, so theres 7.5$ w/ 1 and .5 blinds. he bets 4.5, which is 60% of the pot, so the pot is 12$, 12/4.5 = 2.6
The bet odds are 2.6:1 and the 2cards odds are 2:1 and one card is 4:1.
Since there are still 2 cards to come, I should call since the odds are marginally in my favor, but the one card odds are not in my favor? So if I assume the bet I'll face on the river is atleast 50% of the pot, which means 8$ into 16.5 will be 24.5/8 = 3:1 but my odds are 4:1. This is no longer in my favor, but to justify my call on the flop I should still call this? Otherwise my 2:1 odds are not valid?

Also, should I still devide my % if I have more than 8 outs? I've read this online aswell.

(9*4) - (15 - 9) = 36 - 6 = 30%
(9*2) - (15 - 9) = 18 - 6 = 12%

I've always been bad in math so I'll still make rookie mistakes after so many years, but after a long pause of poker I want to sharpen my game.

You use the 4x rule ONLY on the flop AND an all-in bet, so there is no future betting. You use the 2x rule otherwise. In your example, not an all-in bet, the pot odds are 2.6 to 1 and the odds using the 2x rule are about 4 to 1 so a flop call is not justified on a purely math basis.

Your assumption of a river?? bet has issues. First, the next bet is the turn. Second, your investment has to include the flop call of 4.5 which makes for a higher hurdle. Third, you have to make another guess on river action. Unless you really can anticipate future action correctly, IMO, it's best to use the 2x, 4x rule as recommended above.

Your last paragraph is apparently a correction for the approximate 2x,,4x rule but I don’t recall this particular one. For 9 outs on the flop – all-in, the actual value is 9/47+(1-9/47)*9/46 = 35.0% %, much different from what you show. Check Solomon's rule for one such correction.