Don't be fooled - in "real-time" it's not so simple. Even if you memorized or can calculate the rule of 2 or 4 at lightening speed that gives you a PERCENTAGE. What are you going to do with a PERCENTAGE?
As the pot-odds-for-dummies spells out, the typical pot-odds technique involves ADDING up all chips in the pot and sprayed around the table and DIVIDE by the bet to give an X-to-1. How does this "X-to-1" relate to the PERCENTAGE from the rule of 2-4?
It doesn't. At least not in any way I've found useful in real-time.
Take an example: post-flop, $85 pot, $20 open bet, $20 raise to $40 in front of me. I've got 9 outs. From purely pot-odds break-even point of view, is this a profitable call?
My outs tell me 18% or 36% chance for rule of 2-4, (or I happen to know 19.1% and 34.97% but big deal). That PERCENTAGE doesn't help me make the call. So what good is the rule of 2-4?
As pot-odds-for-dummies and most pot odds sites explain, I better try the math route. Please calculate below at lightening speed:
$85 + $20 + $40 = $145. Divide $145/$40.
Can you do all of this quickly?
I can't. Not without annoying my pals. Especially after a few beers.
Let's hope you could figure out it's between 3 and 4 to 1 because (3 * 40 is $120), and (4 * 40 is $160) so it's somewhere in there.
Calculator says 3.6-to-1.
Too bad you didn't memorize that 9 outs gives 4.22-to-1 for the Turn, and 1.86 with both Turn+River to come.
There are two cards to come, so at 3.6-to-1 winnings and I only need 1.86-to-1 to call right!?
Can I really use the Turn+River outs of 1.86-to-1 to say this is a profitable call *over the two cards*?
As pointed out by various literature, the River card likely won't be free. What bet might come on the river? Should I factor that in and somehow add some future bets to make sure it's break even. That sounds impossible. And therein lies the problem with any Turn+River odds (and the rule of '4'). It's a bust unless there are no more bets to come.
Poker pundits say I could play each draw as if it were my last.
Using only the Turn odds now it's not looking so good: WIN 3.6-to-1 with a 4.22-to-1 chance. Answer: not profitable call for TURN only odds.
EXTRA CREDIT: But wait -- the first to act is reaching for his chips, it looks pretty certain he's going to stay in! Should I recalculate the return with his extra twenty bucks? Yes. Do it. Left as exercise for the student.
How much time did that all take me?
I probably wrote this post faster than I can handle that one single situation. I forgot to even think about stack sizes, implied odds, or even look at the board and think about what my opponents might hold. Fail.