I have a lot more experience with 3rd edition D&D, so many things in Baldur's Gate confuse me.

I'm trying to figure out the maximum amount of HP Jaheira can gain in a level. The highest I've seen after quite a few tries is 11, but her starting HP is 12, which suggests that she'd also be able to gain 12 HP on subsequent levels.

I know in multiclasses, each individual class adds their Hit Die, then divides it by the number of classes in their multiclass they have (then round it down for non-whole numbers, which is only relevant to triple multiclasses).

The part that's likely confusing me the most is whether a Fighter / Druid multiclass build gets the Fighter's Constitution bonus or does not. Jaheira's Constitution is 17, so she just barely qualifies for Fighter's Constitution bonus.

Thanks in advance.

EDIT: I should add, I'm playing the original BG, not Enhanced Edition.

I think she gets it on her fighter levels, but not her druid levels.

But both require the same amount of exp, so they level at the same time.

What she has at the begining is not necessarily correct per rules. You can try creating a fighter/druid with the same stats and check. I believe 11 is the correct amount.

That was an excellent idea for a test (I'm surprised it didn't occur to me before).

The result is that 12 hp actually is the correct amount.

Eh... my memory is fuzzy. HP bonus starts at 15, not 16, so it's max(1d8+1d10)/2+3=12, that's correct.
When both druid and fighter level up at the same time (which happens only during the first few levels), max should be 12. But the chance of getting it is a little over 1%.
I personally dislike the random element and use a tweak to make it nwn-style.
PIHwiki has many details on game mechanics, although I wouldn't dive too deep on first playthrough.

Even so, the HP for the two could be calculated separately and the Constitution bonus added to one and not the other before the two are added together. Though I couldn't swear that's how it works. (Also the classes' advancement XP is the same only for 2nd and 3rd level; after that they diverge.)

A fighter/druid gets 12hp at level 1.

For the fighter half: 10hp, plus 3hp for fighter Constitution, divided in half. 10+3=13/2=6.5

For the druid half: 8hp, plus 2hp for non-profits Constitution, divided in half. 8+2=10/2=5

6.5 + 5 = 11.5 ... Rounded to 12 when displayed on the Character screen. But the game has 11.5 recorded behind the scenes.

Each fighter level can yield 6.5 if you level up with a perfect roll. Each druid level can yield 5 if you level up with a perfect roll. But this will of couse take several reloads and retries to do.

So when you hit level 2 with both classes at the same time, with a max level-up, it'd be 11.5 + 11.5 = 23. The thing to remember is the game keeps track of the decimal, even though the screen displays the rounded-up number.

This is how I remember Jaheira being. Someone correct me if I am wrong.

From what I understand, the way the game handles HP is as follows:

Every character has a base HP value. This value includes rolled HP from level-ups as well as the constant HP gained at high levels. It does *not* include any HP gained from Constitution. A Fighter/Druid gets at most 5 base HP from their Fighter level and 4 from their Druid level; these values are calculated separately and added together to get the character's starting base HP. Note that, since the game (like most games) rounds down, the highest possible roll is less likely than the others, and a roll is more likely. (Correct me if I'm wrong about this.) Remember that Constitution bonus is not factored in here. Hence, our Fighter/Druid starts with up to 9 base HP.

When the game actually checks your HP, the game *then* factors in the Constitution bonus. This bonus is +3 for a character with 17 Constitution, which means that our Fighter/Druid, who is level 1 in both classes, will actually have 12 HP once the game is loaded. For a multi-class character (the rule is different for dual-class characters), if the character has the Fighter or Ranger class, then the character is allowed to get high Constitution bonuses, so we do in fact get the +3. On toe other hand, characters without either class (aside from Paladins and Barbarians, who can't be mult-classed anyway, and Barbarians aren't in BG1 in the first place) will be stuck with the maximum bonus of +2 per level.

Hence, Jaheira can indeed start with 12 HP.

Note that Base HP gains are subject to rounding at every level up; Constitution bonus, however, is not. Therefore, a multi-class character with 15 Constitution will still get that half HP per level up, but it will only appear as 1 HP every other level up. This means that HP will be slightly less on average than if the game didn't round, but the Constitution bonus is not affected.

Note that it is possible for these values to change during gameplay; effects that are listed as granting temporary HP will increase a character's max HP (I think this affects the base HP, but I am not sure if it does or if the game stores it separately), while a change to Constitution will immediately affect the Constitution bonus. There is one exploitable quirk; when maximum HP goes up, current HP does as well, but when maximum HP goes down, current HP does not (except in the case where it would exceed the new maximum); hence, a temporary Constitution increase can sometimes act as healing.

Actually, my point is that is actually doesn't round; the game does not actually store the HP you gained from Con bonuses. Rather, a character's maximum HP is actually derived from the character's Base HP and the combination of Con, class, and level.

However, if what I have said is correct, getting optional HP rolls is less likely than one would expect because of rounding; on a fighter level, she has only a 1 in 10 chance of getting 5 HP (+Con) but a 3 in 10 chance of getting only 1 HP (+Con).

I don't know if gaining multiple level ups at once affects the way HP gains are rounded.

Health per level depends on difficulty setting. Centre ('Normal)' difficulty and above a 10 sided dice is thrown per level, up to level 9 (+3 and +2 thereafter for Jaheira).

Jaheira would be:

1D10 per level Fighter
1D8 per level Druid
+3 Fighter
+2 Druid

These are added and divided by 2 (F/D), rounded down and carried over.

What do you mean when you say 'rounded down and carried over'? The excess that doesn't add up to a whole number is carried over?

Plus 3 and plus 2 do not make an even number (/2), therefore 2 is added at one level and .5 is carried over to the next level, giving +3.

This was also quite intriguing to me, but it was with Montaron and his HP for each class. I decided to do some tests for Jaheira's case. I've installed 'max HP per level up' mod for convenience and here's what I discovered (it kind of proved what I previously thought, but one case is interesting):

I created 3 characters with 17 Constitution: Fighter/Thief, Fighter/Mage and Fighter/Cleric and used cheat codes to gain exact experience points to level up in only one class, then the other and do so again for level 3 for both classes. Each time the characters gained the same amount of HP for given class.

1) Fighter/Thief started with 11 HP total at level one. For Thief class he got 4 HP for each level up, doesn't matter if it's level 2 or 3. For Fighter class he got 7 HP for each level up. So, for level 2/2 he has 22 HP, for level 3/3 - 33 HP and so on.

2) Fighter/Mage is a weird case, he started with 10 HP. I thought that since it's the same Con, he would get 7 for Fighter and 3 for Mage, but to my surprise he got 6 for Fighter and 4 for Mage each time. So, for level 2/2 he has 20 HP and for 3/3 - 30 HP and so on.

3) The last example is the same as Jaheira, because Clerics get the same amount of HP as Druids, but they gain levels faster than fighters, so I can see how many does she get for each class separately. The character started with 12 HP. For Cleric class he got 5 HP for each level up and for Fighter he got 7 HP for each level. So, for level 2/2 he has 24, for level 3/3 - 36 and so on.

I don't think that the 'max HP per level' has influenced the results, because it only changes each roll to be max possible. The mechanics itself should be the same.

I always thought that the max possible HP for each level is the same as HP on level 1, no matter what level the multiclassed character advances to. It seems to me that the bonus for Con is divided between the classes, especially since in that second character got 4 HP for Mage and it's just strange to me. I remember that when a character advanced in both classes at the same time it was almost impossible to get the max possible HP total, it seems that it's just two separate rolls and therefore chance for getting max HP is very small.