Wednesday, April 23, 2008

Multiclass Hit Points

You know, it turns out that I always did multiclass hit points in AD&D incorrectly.

If you look at AD&D PHB p. 19, there's a procedure for multiclass hit points laid out. It says, in summary, to (1) "Roll the hit die (or dice) appropriate to each class the character is professing", (2) "Total the sum of all dice so rolled, and adjust for constitution", (3) Divide by the number of classes, and (4) Add that many hit points to the character's total.

Let's take an example. You've got a 1st-level Clr/Ftr who goes up a level in Cleric (assume no Con bonus). I always thought, by this plan, that you'd roll (d8+d10)/2 and add that to hit points, and do the same thing over again when he goes up a level in Fighter. Note that over the course of that you've effectively gotten the full hit dice for each class level, it's just smoothed out over each level increase. So effectively my multiclass characters all had hit points equal to the sum of all class levels they had, and had enormous hit points compared to their fellow characters.

Here's the glitch. I'm pretty sure now that you should only roll the hit die for the single class being increased at any step (and still divide by the number of classes). Now, maybe I misread step #1. Or maybe that paragraph was written thinking that a step up in level always occured simultaneously in all of the classes (which isn't the case because you've got different XP charts for each class). Either way you slice that, you should really be getting effectively the average of all their class levels, which is a lot more reasonable, and not totally outstrip single-class characters with the same total XP.

Here's what clinched it for me when I realized this possible discrepency. I actually went and made a spreadsheet, entered the data for every single pregenerated multiclass PC in any AD&D adventure module, plus the 100 multiclass characters appearing in the Rogues' Gallery. I computed the expected HP value for each character under each interpretation, and calculated the total sum-squared-errors for each option. Result: My old interpretation was way off compared to what appears on average in the books. Sum-squared errors for the module PCs was 8,690 vs. 668; for the Rogues Gallery characters it was 8,884 vs. 363. Clearly the second "averaging" interpretation was much closer to the mark.

If you like you can download the analysis spreadsheet here:

(P.S. I'd also entertain a "maximum" operation for hit points where you roll hit points for each class separately and take whichever is currently highest. Pros: (1) Consistent with all other "max" operations for attacks, saves, proficiencies, etc.; (2) Would allow multiclassers to catch up a bit in HP compared to higher-level single-classers. Cons: (1) You'd have to track & record multiple class HP rolls, and (2) That one's clearly not supported by the rules-as-written.)


  1. "Roll the hit die (or dice) appropriate to each class the character is pro[gr]essing"

    Sure, the XP seldom exactly lines up, but (IME) you usually only level up between sessions. Or between expeditions--if your using the training rules. There's a decent chance that during a single session/expedition you'll occasionally cross the threshold for more than one class.

    I think the fact that "dice" is in parenthesis and "die" is not supports this.

    One thing about the oAD&D PHB is that it doesn't want a PC to gain more than 9HD (or the equivalent). Check out the "character with two classes" (which would come to be known as "dual classing") section too.

    The rule I plan to use for "dual classing" in classic D&D, if it ever comes up, is that the player keeps a separate hp total for all his classes, but only the highest one is in effect. (In 3e terms, they don't stack.)

    e.g. An MU-4/Fighter-1 might have 10 MU hp and 8 Fighter hp. So, he'd use the 10 in play. Once he became a MU-4/Fighter-2, however, his Fighter hp might be 15, so then he'd use 15 in play instead.

  2. Ouch. Yeah, using that method would certainly make multi-classing very attractive. My more experienced AD&D players rarely ever multi-classed. Nothing beats a straight Fighter for hit points.

    I've seen others on the 'net saying that you should always multi-class in AD&D, and I wonder if they too rolled hit points improperly. Interesting post.

    After reading what you quoted from the PHB, you probably could have convinced me that I was doing it wrong!


  3. How do you pick which class gets the XP? Wouldn't a split or dual class character be able to use abilities from either class at any time? Isn't that the point?

  4. "How do you pick which class gets the XP? Wouldn't a split or dual class character be able to use abilities from either class at any time?"

    This post is solely about the multiclass hit point issue. Presumably all other normal AD&D rules apply (XP split evenly; abilities used at any time).