# Do Monsters gain Maximum HP when they gain Hit Dice?

Player Characters gain hit points each time that they level up in addition to a corresponding increase in maximum health points.

What about monsters though? If a monster gains hit-dice, does it also gain maximum hit points?

To put it differently, are hit-dice the source of maximum HP or are they simply gained alongside an increase in max-HP?

As an example, the Nabassu (as described in this question), gains hit dice when it uses its Devour Soul feature, however it's unclear to me whether it would also gain max-HP.

# A monster's hit points are derived from their hit dice

From the introduction to the Monster Manual on Hit Points (p. 7):

A monster's hit points are presented both as a die expression and as an average number. [...]

A monster's Constitution modifier also affects the number of hit points it has. Its Constitution modifier is multiplied by the number of Hit Dice it possesses, and the result is added to its hit points. For example, if a monster has a Constitution of 12 (+1 modifier) and 2d8 Hit Dice, it has 2d8 + 2 hit points (average 11).

The wording of the latter paragraph, and in particular the example, use that a creature's hit points come its hit dice, with a bonus from the constitution modifier (the single number commonly used is the average of hit point representation). Following that logic, adding more dice should increase the creatures hit points. It is worth noting that this is the same logic in the guidelines for creating a monster (ignoring the method which is singly give it a number of hit points) on page 276 of the Dungeon Master's Guide. The creature is assigned a number of hit dice (the size determined by the creature size) which then gives its hit points.

For the specific example, the Nabassu's feature includes (emphasis mine):

Roll those dice, and increase the nabassu's hit points by the numbers rolled.

Which gives an explicit for how the new hit dice affects the number of hit points. Note that it says "increase" and not that it regains hit points, meaning meaning the number of hitpoints should be increased, irrespective of whether any hit points have been lost previous.

• It may be worth looking at this question about whether a monster changing size changes its hit points, where the answer is not because size is only relevant for the initial HP calculation. I'm unsure whether or not it goes against your answer since they have similar wording: "A monster's size determines the die used to calculate its hit points" vs "A monster's Constitution modifier also affects the number of hit points it has." Then again, that may be entirely irrelevant, I'm honestly unsure – Medix2 Jan 6 '20 at 21:12
• I seriously question this: "hit dice and the actual hit points it has are two expressions of the same." At best, very awkward phrasing; at worst, just wrong. The rest of the advice (roll the dice, do not default to maximum) is correct, but I'll probably downvote if that phrasing persists. – Novak Jan 6 '20 at 21:51
• Might be worth noting that the ability doesn't say to increase maximum hit points, which is why I deleted my answer addressing the same point. Unlike many previous editions, rather than having "hp" and "damage taken", 5e tracks "current hit points" and "maximum hp", and most things that just say "hit points" refer to current rather than max. – gatherer818 Jan 7 '20 at 8:03
• @gatherer818 given that maximum hit points are directly derived from hit dice, it would be rather illogical to posit that its hit point maximum does not increase when it gains more hit dice, even if those hit dice are temporary, but as it doesn't explicitly state the max HP increase, it could go either way. One other thing that is notable, is that it doesn't get to add its Con modifier to these extra hit points when they are rolled. – RevanantBacon Jan 13 '20 at 19:31