[RPG] The Beast Master ranger adds their proficiency bonus to their animal companion’s AC; is the result its new base AC

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As per the Ranger Companion feature, you can add your proficiency bonus to your companion's AC.

I would like to know how to interpret this in terms of AC calculation.

Could I interpret as though my pet is getting a bonus to its base AC (Example: A PC wearing a shield). Or is this new number the new base AC?

In terms of formulas, let's take the Wolf:

AC = 13 (natural armor)

AC with Ranger Companion at level 3 = 15 (13[base] + 2[Prof])

The second interpretation would be that the wolf's new base AC simply 15.

The way the feature is worded makes me believe it's the former. The reason I ask this is to understand how this would interact with spells like Barkskin.

Barkskin states that your AC cannot be less than 16, meaning that if you choose to use Barkskin as the way you calculate your AC, it is now 16. You can choose to wear a shield on top of Barkskin, and receive the bonus as normal, meaning, it'd be 18 AC total.

Now let's go back to the Wolf. If the former interpretation is true, and I apply Barkskin to my wolf, that'd mean his base AC can now be 16 instead of 13, and in addition to this he receives a bonus to his armor class equal to my Proficiency bonus. Assuming level 3 ranger, that'd mean my wolf's armor class is now 18.

Otherwise, if the latter is true, then his AC is 16 while under barkskin but he does not receive the bonus because the latter interpretation states that the bonus is simply part of his base AC calculation instead of an additional amount of AC he gets because of the feature.

Best Answer

No, the base AC of the Wolf remains 10+1+2 (13), if a game effect changes the base AC it says so in the text.

You add your proficiency bonus to the beast’s AC. You do not change the Wolf's base AC to 13 + your proficiency bonus. In other words: the base AC of the Wolf (MM 341) remains 13 (10+1 from natural armour, +2 from Dexterity), and the total is 15 (10+1 from natural armour, +2 from Dexterity, +2 from the Ranger's proficiency which increases further at higher level, see PHB page 15), for natural armour see MM (page 7) and for general armour-class calculation see the SA Compendium V2.3 (page 2).

Add your proficiency bonus to the beast’s AC, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in. (PHB 93)

How Barkskin works (PHB 217) If your Wolf's AC is less than 16, it is now 16. 15 is less than 16, it now is 16 as long as the duration of Barkskin remains maintained. If it is higher than 16, then Barkskin does not grant additional AC, it merely prevents the AC from going below 16.

the target's AC can't be less than 16

So multiple of your assumptions are incorrect, Barkskin does not change your Wolf's base AC, neither does the Ranger's Companion feature change your Wolf's base AC.

A spell that changes your (Wolf's) base AC would be, for instance, Mage Armor (PHB 256):

The target’s base AC becomes 13 + its Dexterity modifier.

Whenever a game effect changes the base AC, it states explicitly that.

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