The Rule of 4 and 2.
The rule of 4 and 2 (or the 2/4 rule, whatever you want to call it) was coined by Phil Gordon in his Little Green Book, which is an awesome little strategy book for NL Hold’em by the way.
In this article I will explain what the rule of 2 and 4 is all about and show you how to use it during play.
What is the rule of 4 and 2?
The rule of 4 and 2 is a quick shortcut for helping you to work out the percentage odds of completing a draw in Hold’em. To get your percentage odds:
- Multiply your outs by 2 when you are on the flop waiting for the turn.
- Multiply your outs by 2 when you are on the turn waiting for the river.
- Multiply your outs by 4 when you are on the flop waiting for the river (opponent is all-in).
When you have multiplied your outs by either 4 or 2, you will get a percentage that you can compare with your pot odds to work out whether or not it’s worth calling with a drawing hand.
The rule of 4 and 2 just works for percentages odds, not for ratio odds I'm afraid.
Examples of the 2/4 rule.
- Flush draw: 9 outs * 2 = 18%
- Straight draw: 8 outs * 2 = 16%
- Two overcards: 6 outs * 2 = 12%
- Two pair and you need to make a full house: 4 outs * 2 = 8%
- Flush draw, opponent is all in on flop: 9 outs * 4 = 36%
- Straight draw, opponent is all in on flop: 8 outs * 4 = 32%
Easy stuff really. As long as you know your 2 and 4 times tables you're all set.
Important — You rarely multiply by 4.
Even though it’s call the "rule of 4 and 2", it should really be called the "rule of 2 (and 4 on rare occasions)", but that’s obviously less catchy. Too many players make the mistake of using the 4 rule on the flop every time, and they lose a lot of money because of it.
The only time you should ever multiply your outs by 4 is when you are on the flop and your opponent has moved all-in. Therefore, you do not expect to face another bet on the turn that will force you to pay more to try and complete your draw.
Basically, always look to multiply your outs by 2 when you are on the flop or the turn to get your correct percentage odds. In the unlikely event that your opponent moves all-in on the flop, then you can dust off the rule of 4 and enjoy its company for a brief moment.
Hand examples of the rule of 4 and 2.
Hand example 1.
You have a flush draw on the flop in a $0.50/$1 NL Hold’em game. Your opponent bets $10 in to the $10 pot. The pot is now $20 and you have to call $10 to continue to try and hit your flush. Should you call or fold?
Hand: A 2
Board: J 3 7
Final Pot: $20
To Call: $10
With a flush draw we have 9 outs, and seeing as we are on the flop waiting for the turn, we will use the "rule of 2".
- Odds of completing our flush: 9 outs * 2 = 18%
- Pot odds: 33% ($30 pot total including our call. $10 is 33% of $30.)
Note: Don’t forget to add your potential call to the pot size when working out percentage odds. It’s a little different to the way we work out ratio odds I know, but try and get used to it. Look over the pot odds article to remind yourself.
The odds of completing our flush are worse than the odds we are getting from the pot, therefore we should fold. To put it another way, we do not want to call more than 18% of the pot size to continue, so we fold.
Hand example 2.
You have two overcards on the flop in a $0.50/$1 NL Hold’em game. Your opponent moves all-in for $10 in to the $30 pot. The pot is now $40 and you have to call $10 to continue. Should you call or fold?
Hand: A Q
Board: J 3 7
Final Pot: $30
To Call: $10
It’s one of those rare occasions where our opponent is all in on the flop, so time to whip out that "rule of 4" for once. Let’s also assume that if we pair one of our overcards that we will definitely have a better hand than our opponent.
- Odds of winning: 6 outs * 4 = 24%
- Pot odds: 20% ($50 pot total including our call. $10 is 20% of $50.)
As it turns out, our odds of winning this hand are better than the odds we are getting from the pot; therefore it is profitable for us to call in an attempt to make an overpair in this example. To put it another way, we can call up to 24% of the pot size to continue, so we call.
Rule of 4 and 2 accuracy comparison tables.
Just so you can get an idea of how accurate the rule of 4 and 2 is, here are two tables that compare the percentage odds you get using the rule of 4 and 2 and the actual percentage odds for the most common types of draws in Texas Hold'em.
Rule of 4 accuracy table.
|Outs||4 and 2||Actual||Difference|
|15 (straight + flush)||60%||54.1%||+5.9%|
The percentage odds are impressively close when using the rule of 4 (i.e. when your opponent is all-in on the flop and there are two cards to come).
The only draw that's noticeably off is the straight + flush draw when you have 15 outs (5.9% difference), but that doesn't really matter because when you've got a greater than 50% chance of winning the pot it makes it +EV to call absolutely any size bet anyway.
Rule of 2 accuracy table.
The rule of 2 can be used on both the flop and the turn. So to keep things simple, in the following table I'll just compare the percentage odds for when we are on the turn waiting for the river.
|Outs||4 and 2||Actual||Difference|
|15 (straight + flush)||30%||32.6%||-2.6%|
Not bad, although not quite as accurate as the rule of 4.
Still, if the rule of 2 stops you from fumbling around with working out the exact odds and in turn accidentally making a bad decision then it has done its job. Furthermore, 1% or 2% under the actual odds is hardly going to lead you to making a terrible play, so I honestly wouldn't worry about it.
Note: The percentage odds when using the rule of 2 on the flop are slightly more accurate than when you're using the rule on the turn (as shown in the table above).
Evaluation of the rule of 4 and 2.
The 2/4 rule is as good as rule are you are going to get for quickly working out percentage odds with drawing hands.
As long as you know how to work out pot odds as a percentage and you prefer working with percentages over ratios, this is the most useful rule you could hope to find.
As far as accuracy goes, the actual percentages are very close to the percentages the rule of 4 and 2 gives out. There are obviously differences of around 1% either side for most draws, but the difference is not big enough to worry about in my opinion. The simplicity and speed that the rule offers more than makes up for the slight decrease in accuracy with odds.
In my main article on pot odds I preferred to use the "rule of 2" plus 1, which is ever so slightly more accurate. At the end of the day though, the rule of 4 and 2 is the quickest shortcut method that you’re ever going to find for working out percentage odds without taking a much longer route for a similar result.
Phil Gordon also coined the Gordon Pair Principle.