Why we use geometric bet sizing
Dara O'Kearney explains what pot geometry is and why we use it across multiple streets of a poker hand.
A couple of students have recently asked me about geometric bet sizing and why we do it. Why is it we increase our bet sizes and the percentage of pot sizes on different streets?
Geometric bet sizing refers to the correlation between the bet sizes on different streets and the final pot size.
The reason we use geometric bet sizes is they maximise the amount of times we win our opponent's entire stack, assuming they defend at the right frequency on each street. Remember that bluffing is overrated in poker and we are trying build a strategy around our value bets. That means taking our opponent's stack size into consideration, not just the pot size.
Solvers use geometric bet sizing all the time and in some cases of deep stacked spots you will see them make overbets or check/raises on one or more streets in order get the stacks in by the river.
Always target your opponent's stack
Let's look at two examples. In example one the effective stacks are 50BBs, you minraise the pot UTG and get called by the Big Blind. There are 4.5BBs in the pot on the flop and you bet 3BBs (66% pot), you get called.
The pot is now 10.5BBs and on the turn you bet 7BBs (66% pot), you get called. The pot is now 24.5BBs and you have 38BBs behind.
On the river you now have more behind than there is in the pot. If you have a value hand you have to overbet to get the whole stack. If you continue with your 66% pot size strategy you will only win just under 41BBs if you get called by worse.
If, however, you opened to 2.5BBs preflop, the pot on the flop would be 5.5. If you then bet 4.5BBs (82% pot) on the flop the pot on the turn would be 14.5BBs. Make your turn bet 13BBs (90% pot) and if you get called the river pot size is 40.5 and you have 30BBs behind. You can now shove the river for 74% pot and are more likely to get called.
You don't have to worry so much in shallow stack spots because those are easy to get all-in by the river, but in deep stack pots with your best value hands you don't want to leave money on the table. You have to do creative things like check/raise and overbet (as well as picking the best bluffs to do the same thing with) to set up bets your opponent will call often enough on the river.
A lot of people make the error of thinking solvers try to play 'break even' or defensive poker, when nothing is further from the truth. Solvers are always trying to take the opponent's whole stack with their best value hands and they do this by setting up their bet sizes strategically across multiple streets.
Dara O'Kearney's new book GTO Poker Simplified is out now.
