The Rule of 4 and 2, and when to ignore it
A fast way to turn your outs into a rough equity estimate at the table — plus the adjustment that separates players who memorized the rule from players who understand it.
You flop a flush draw. Nine cards complete it. What’s your chance of getting there? You don’t need a solver — you need arithmetic you can do in three seconds.
The rule
- On the flop, with two cards to come: multiply your outs by 4.
- On the turn, with one card to come: multiply your outs by 2.
Nine outs on the flop → roughly 36% to hit by the river. Nine outs on the turn → roughly 18%. Close enough to the real numbers (35% and 19.6%) to make decisions with.
Turning equity into a decision
Equity alone doesn’t tell you to call — you compare it to your pot odds. If calling 20 into a pot of 60, you’re getting 3:1 and need to be right 25% of the time. With 36% equity, that’s an easy call.
outs × 4 ≈ flop equity %
outs × 2 ≈ turn equity %
call if: equity % > amount to call / (pot + amount to call)When to ignore it
Here’s the part most players skip. The Rule of 4 and 2 assumes all your outs are good and that you’ll get to see the river. Neither is guaranteed.
Against Pete the fish, who calls every street, your draw is worth full price — he pays you off when you hit. Against Kim the nit, who only bets strength, some of your “outs” complete her better hand, and she’ll charge you the turn so you rarely see the river cheaply.
Same nine outs. Different opponents. Different decision.
That’s the difference between memorizing the rule and understanding it — and it’s exactly what Hone grades you on: not the math in a vacuum, but the right play against these players in this spot.