As players begin dipping into the world of GTO, one of the first concepts they come across is MDF. And while MDF and GTO certainly have some overlap in their frequencies, there are some simple ideas that need to be 100% understood.
What Is MDF?
MDF, short for minimum defense frequency, attempts to tell you how much of your range you need to continue with (either by calling or raising) in order to ensure your opponent cannot auto-profit from bluffing you excessively.
What Is The MDF Formula?
You only need two numbers to calculate MDF. The MDF formula is simply:
So if the pot size (before their bet) is $100, and villain bets $50, the MDF would be 67%. Meaning MDF states that you need to continue at least 67% of the time to not allow your opponent to make auto-profit when bluffing you.
Free MDF Calculator
If you want to do your own MDF calculations, you can use this free calculator. Just plug in the pot size (before villain bets) and their bet size.
You can download an offline version of this tool, along with 20+ others, in my free poker spreadsheet pack. Get EV calculators, pot odds, implied odds, and more!
Using MDF When OOP
Although the concept of MDF is loosely based around GTO poker, there are some key issues with the approach:
- An MDF calculation may differ significantly from the correct GTO defending frequency.
- A frequency itself does not tell us which types of hands to defend and how.
Let us consider how far off our defending frequencies would be if we were rigidly adhering to MDF in the formation in which BTN opens and BB defends.
Here are the GTO defending frequencies against a range of different c-bet sizings that might be used by the BTN.
MDF BB vs BTN
| Sizing | MDF | GTODF |
| 33% | 75.2% | 65.6% |
| 50% | 66.7% | 57.2% |
| 75% | 57.1% | 48.4% |
| 125% | 44.4% | 36.8% |
We learn that GTO defending frequencies are consistently lower than MDF calculated values. If we use MDF to derive our flop defense in this scenario, we will be defending significantly too wide.
A simple rule of thumb might be that we should fold around 10% more often than MDF would suggest when playing as the cold caller OOP.
It is important to acknowledge that formation plays a role here:
- We fold slightly more in general when the original opener was in an earlier position.
- We fold slightly less when we are the SB cold-caller as opposed to the BB cold-caller.
For example, SB cold caller vs a BTN c-bet only folds a few percentage points above MDF, while BB cold caller vs UTG c-bet folds almost 15% above MDF.
Using MDF When In-Position
This is not to say that MDF calculations are way off in every scenario.
When we analyze the data for defending IP, we find that the defending frequencies correlate closely with the respective MDF values.
MDF IP Table
| Sizing | MDF | GTODF |
| 33% | 75.2% | 74.7% |
| 50% | 66.7% | 65.9% |
| 75% | 57.1% | 56.0% |
| 125% | 44.4% | 42.8% |
Although there will once again be formational differences, defending at around the MDF value is fairly consistent when playing IP as the defender.
We observe a similar relationship to MDF when playing as the defender in 3-bet pots.
An IP defender defends close to MDF, while an OOP defender will be โoverfoldingโ according to MDF to a degree that depends on the precise formation and board texture.
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The MDF Thought Experiment
Many players struggle with the idea that the IP aggressor is now generating automatic profit when they continuation bet against us.
โThe point of GTO defense is to prevent our opponent from generating automatic profit, correct?โ
From the perspective of the entire game tree, the answer is yes.
However, from the perspective of an individual hand, the answer is a clear no.
Consider the following thought experiment which exposes the weakness of MDF calculations.
Imagine our opponentโs range on the river is exclusively full houses. Our range is exclusively mid pairs. Our opponent bets pot size on the river.
What is:
- Our MDF?
- Our GTO-correct defending frequency?
According to MDF we need to defend our mid pair 50% of the time, despite the fact that we will always lose when defending.
The GTO-correct defending frequency is 0%. GTO would never call if the EV is negative, even if the end result is automatic profit for villain.
We learn that it is acceptable to give our opponent automatic profit. When the roles are reversed, our own strategy will generate an equivalent amount of automatic profit against villain.
The net result in a perfect GTO game is zero profit across the entire game tree.
Automatic profit in individual hands is a common feature of GTO play, however, which is why the concept of MDF becomes unreliable.
Conclusion: MDF & GTO
Understanding the nuances between MDF and GTO is crucial. While MDF offers a simple defensive framework, GTO provides a comprehensive strategy considering multiple game aspects.
For a deeper understanding, check out GTO Gems 2 available online and in paperback on Amazon.
