# Calculating Hit Points past Level 1 [duplicate]

What is giving me trouble is the phrase

+ your Constitution modifier per [class] level after 1st.

Does this simply mean I add my CON modifier once each time I level up, or add my CON modifier a number of times equal to my class level?

• @TuggyNE: I feel like there needs to be some sort of agreement which one is going to be marked as a duplicate of the other here... :P
– V2Blast
Jul 7 '18 at 8:41
• @V2Blast: The one with the better answers. If there's no real difference, the one with the better question. If there's no real difference, the older or more popular or better-linked one. Jul 7 '18 at 8:45

Each time you gain a level you will add your constitution modifier and one roll of your hit die to your previous max HP. If a barbarian with 18 constitution levels up he takes his previous max plus a roll of a d12 plus 4 for his constitution modifier.

On a related note if your CON modifier increases later you gain hit points retroactively for all previous levels.

I have to agree that the wording is a bit convoluted or rather short in the class definitions. However, it is clarified in PHB p. 177:

If your constitution modifier changes, your hit point maximum changes as well, as though you had the new modifier from the 1st level. [...]

(And where some people may get quite wrongly confused, the example they give is positive and not negative... but unfortunately, it does go both ways.)

The math is pretty straight forward and can be expressed as follow:

In my formula, I put a minimum of 1 HP per level which does not appear in the PHB, at least not for HP. But there are various places where that max() function is used. For example, in PHB p. 84, the Paladin Spellcasting ability says that the Paladin gets a number of spells equal to:

[...] Charisma modifier + half your Paladin level, rounded down (minimum of one spell) [...]

There is also the Enlarge/Reduce spell in PHB p. 237 which says (very end):

[...] (this can't reduce the damage below 1).

Also, without the minimum, you could end up dead just and only because you lose your constitution (i.e. a really bad constitution of 1 would give you a -5 modifier, so at level 20, you would lose 100 HP from your rolls... and if your maximum was close to 100 [sorcerers and wizards have 1d6 or an average of 4 × level... would 80 HP - 100 HP = -20 HP], you would die right there.)

As a side note, that applies to all effects that make use of a modifier. So you could lose spells you've learn before because your Intelligence decreases. Similarly, and quite important, your Dexterity could decrease and thus does your AC. That is much more common than losing constitution or intelligence (also, you may want to read Feeblemind, PHB p. 239 in link with abilities going to 1, some magical treasures also have such wonderful effects...)

As pointed out by Miniman, some creatures (Vampire, Wright) and spells (Harm) may reduce your maximum number of hit points. In that case, this reduction has nothing to do with your constitution nor your level, however, it can further complicate your HP math.

• So you are saying that if I level up I may get 0 or even -1 HP for gaining a level? Feb 18 '15 at 5:49
• Sorry, it appeared that you were talking about what happens when your Con decreases. That said, with a sufficiently low Con modifier there's no reason you couldn't gain 0 or less max hp on level up. Feb 18 '15 at 6:02
• Alexis, this seems to be responding about con changes, but the asker only wanted to know if they add their con modifier onto their new level's HP gain once, or once per class level they have: i.e. nothing to do with con changes. That would make this not an answer. However, if you still want to preserve this writing, you could create a self-answered question for this content. Feb 18 '15 at 6:35
• @Alexis Because CON changing isn't something the asker's confused about or considering. I've reread your answer and it seems it isn't as not-an-answer as I thought, but it's still off target and wandering into issues that aren't even present here. They're asking, assuming a particular hit die and CON modifier: "This thing says to add my constitution modifier per class level. When I hit level 3, do they mean I add 1d8 + 4 health, or do they mean I add 1d8 + (4 + 4 + 4) health?" Feb 18 '15 at 7:20
• The formula is correct (assuming HP gained per level has a minimum of 1). It just has way too much tangential discussion around it, making it unclear what part of the answer contains the answer. It makes sense to me and I didn't downvote it, but I can see why it might not be understandable to someone who doesn't already know the answer or someone who can't read sigma notation. Feb 18 '15 at 16:11