Toughness Bonuses: When to take or Pass

One of my favorite things about playing Chaos Marines is their customizable options.  When working with marines and cultists Chaos has the option to buy an additional toughness with a mark of Nurgle.  The difficult part is determining when this is a good idea vs when should you add more models.  I am here with math to help you all figure things out.


I am going to focus exclusively on squads of models rather than special characters because you can't add additional characters in most cases.

The charts that I use talk about increased durability versus a particular strength of attack.  As long as the percent increase of durability is greater than the percent increase in cost of an additional model then a mark of nurgle is going to be more efficient for overall survivability than adding additional models.

Adding additional models does also increase the damage output for a unit, but that is a conversation for another time

Toughness 3: Cultists
Mark of Nurgle add a staggering 50% to the cost of each individual model, so in order for the upgrade to be worth the cost we need it to make our model at least 50% more durable.

Strength	Durability Increase
1	0%
2	100%
3	50%
4	33%
5	25%
6+	0%

So the only times where mark of Nurgle is worth the cost is when the attacks are strength 2 or 3.  Since most people aren't worried about these attacks it is almost always better to buy additional cultists rather than using the mark of Nurgle.

Toughness 4: Marines, Chosen, Terminators, Raptors, Possessed, Warp Talons

When we look at the toughness four models in the Chaos codex we see quite a few more options, and as a result some varying levels of effectiveness for the mark of Nurgle.  All toughness four models will get the same durability increase, but the increase in their points will vary.

Strength	Durability Increase
2	0%
3	100%
4	50%
5	33%
6	25%
7+	0%

This is more or less the same chart as was used for the cultists, but all of the strength values have increased by one.

Standard marines are relatively inexpensive, but mark of Nurgle will increase their points by 23%.  This means that a mark of Nurgle is going to be effective against any attack that is less than strength 7.  Chosen increase their cost by 16%, terminators by 19%, Possessed by 15%, raptors by 17% and Warp Talons by 13%; as long as you aren't getting hit by S7+ weapons a mark of Nurgle is mathematically worth the points.

I know some readers are thinking, "My terminators only get shot by plasma guns, how does this information help me?"  I will talk about shooting from mixed weapons in the next section.

Toughness 5: Spawn, Bikes

Once again we have the same chart as before, but since the starting toughness is higher the strength values have increased as well.

Strength	Durability Increase
3	0%
4	100%
5	50%
6	33%
7	25%
8+	0%

A mark of Nurgle for chaos spawn only increase their cost by 20%, so it is effective against anything but strength 8 and above.

Bikes pay 30% of their original cost for a mark of Nurgle.  This immediately means that it isn't as effective as adding additional bodies when the strength is 7 or above.  

Mixed Shooting:

Most of the time a unit gets shot it will have multiple types of incoming fire.  This could be from special weapons in a squad or it could be because they are taking fired from more than one squad.

Lets say I have a squad of terminators that I know is going to get shot up by marines with plasma guns.  A mark of nurgle will increase survivability from the bolters, but won't help with the plasma.  Here is how this gets calculated:

A squad of 10 guys with 2 plasma guns will have 80% of their shots from bolters and 20% of their shots from plasma.

80% of shots have 50% damage reduction and 20% of shots have 0% damage reduction.

0.8*0.5+0.2*0=0.4

So there is an overall damage reduction of 40%.  So it is still more efficient to purchase a mark of Nurgle before adding additional terminators.

For another example: A squad of bikes is likely to get shot by an ion cannon and smart missiles from a hammerhead.  The 8 smart missiles make up 73.7% of the shots and the ion cannon makes up 27.3%.

73.7% of the shots have a 50% damage reduction and 27.3% of the shots have a 25% damage reduction.

0.737*0.5+0.273*0.25= 0.432 or an overall reduction in damage of 43.2%.


Putting it all together:
When looking at a mark of Nurgle in most isolated situations, it is more efficient at increasing durability than adding additional models.  The increased survivability from the mark outweighs the increased survivability of adding more models to a unit.

In future articles I want to look at defense vs offense of adding bodies and marks of Nurgle to get a better overall perspective.

**Updated with the numbers for Raptors**