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OTB #015: Why MDF is more useful on the turn and how to use it to be tougher to play against

Updated: Mar 18

Minimum defence frequency (or MDF) is a way of working out how often you should continue facing a bet to avoid being exploitable to bluffs.

Minimum defence frequency = pot size / (pot size + bet size)

If the pot is 550 and your opponent bets 275 (1/2 pot) then the MDF in this spot is worked out as:

550 / (550 + 275) = 550 / 825 = ~66.7%

This means that you need to continue with at least 66.7% of your range and therefore fold 33.3%.

Here's a table of common bet sizes and how often you should continue against each:

If you face a 1.5x pot bet, you need to continue with 40% of your range. If you face a 3/4 pot bet, you need to continue with 57.4%.

It's not that simple though...

Today I want to give you two tips when it comes to understanding the concept and application of minimum defence frequency to make you tougher to play against postflop:

1) Do not use MDF on the flop when you have the much weaker range

2) Get close to MDF on the turn once you call and the equities run a lot closer together

Let's look at each tip in turn...

1) Do not use MDF on the flop when you have the much weaker range

MP opens and you defend in the BB with Ac4c.

The flop comes Ah Ks 3h and you check. MP bets 2.5bb into 5.41bb.

According to MDF, how often should you continue here?

Pot size = 5.41bb, Bet size = 2.5bb

MDF in this spot = 5.41bb / ( (5.41bb + 2.5bb) = 68.4%

Quick tip: To work this out quicker, look at the replayer above and take the pot size next to the cards (5.41bb), which is the pot size before the bet, and then divide that by the total pot size after the bet at the top of the screen (7.91bb).

If you were blindly going to follow the idea of MDF you should continue (either by calling or raising) with 68.4% of your range and fold 31.6%.

And yet a solver wants you to fold ~50%:

So what's going on here?

MP's equity when they bet is 67.9%, which means yours is just 32.1%.

Your range is much weaker and that means you should overfold and not try to hit MDF.

You should continue:

  • All sets

  • All two pair

  • All top pair

  • All 2nd pair

  • 3rd pair with a backdoor flush draw (i.e. JJ/TT with a heart and 3x of spades)

  • All combo and flush draws

  • Most 4 out straight draws

And you can fold:

  • 3rd pair with no backdoor flush draw

  • Some 4 out straight draws (QJ/QT/JT no heart sometimes fold)

  • Everything else

If you tried to hit the MDF in this spot you'd end up having to call with the 3rd pairs and all the straight draws and then some random hands with two spades. Imagine taking that range to the turn against a player with the much stronger range.

Remember, you shouldn't try to use the concept of MDF on the flop when you have the much weaker range.

2) Get close to MDF on the turn once you call and the equities run a lot closer together

You call the c-bet on the flop and even before you see a turn card, it's important to discuss what happens with equities here.

You have folded a lot of hands, most of them weak, whereas the MP player can still have some weak hands as well as some very strong ones and then some in the middle too.

Facing the 2.5bb c-bet on the flop your range had just 32.1% equity, but after you fold so many weak hands your equity jumps up to 49.8% when you call the c-bet. And that's even before you've seen a turn card.

Here's the "Runouts EV Comparison" to compare equities on the different turn cards:

Your equity is different depending on the turn card: hearts and low cards are the standout cards for you.

You check and MP bets again, 5.82bb this time into a pot of 10.42bb.

The minimum defence frequency on the turn is worked out as:

10.42bb / 16.24bb = 64.16%

That means you should fold ~36% of the time.

Below are the average frequencies for folding, calling, raising and jamming (from bottom to top) across all possible turn cards:

The average folding frequency is very close to the minimum defence frequency.

However, there is a wide spread of folding frequencies from 31.51% on the 6s up to 46.44% on the Ac and Ad.

Generally speaking, the better the turn card for your range, the more you should continue.

It's not a perfect approach though because the Ac is not that bad, but has the highest frequency of folds. On this card the MP player will have a slightly higher proportion of nutted hands and will have more equity with those hands too.

On the 9h specifically you want to fold 39.05%, call 51.45%, raise 9.49% and jam 0.00%. This means continuing ~61% of your range.

In order to hit that frequency you need to continue:

  • All flushes

  • All two pair

  • Most top pairs

  • Some 2nd pairs

  • All 3rd pairs (JJ and TT with a heart)

  • Most combo draws (QJ/QT/JT with a heart all continue, 54o with a heart sometimes folds)

  • All flush draws

And you can fold:

  • All 3rd pairs

  • All 4 out straight draws (that don't have a flush draw)

This week's action tip: Check your fold to turn c-bet frequency OOP.

Your folding frequency shouldn't be any higher than 50% because:

  • Most low- and mid-stakes MTT players double barrel for less than a pot-sized bet on the turn regardless of stack size and stack to pot ratio

  • At 40bb and under, the geometric sizing for a turn double barrel after a 25% pot flop c-bet is less than pot.

If it's higher than 50% you have a leak and need to be more sticky on the turn.

You want to be tough to play against and you can do that by making sure you are sticky enough on flops, turns and rivers.

However, it's important you remember to think about these two tips:

1) Do not use MDF on the flop when you have the much weaker range, but...

2) Get close to MDF on the turn once you call and the equities run a lot closer together

Good luck!


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