I've learned that I can level-up, check to see if I got the HP I want, and if not, reload and try again. I did this a few times and ended up getting extra HP, but I realized I don't really know the min/max HP available. What is the range, and does it change with race/class/level, or anything else? Edit: I do know that Constitution has an effect on level-up HP, but I can't change that early in the game.

Depends on the class.

Wizards get max of 4 +CON modifier (max +2 for this)
Warriors get max 10 + CON modifier
Cleric and Druid 8 + CON modifier (max +2 for this)
Thief and Bard max 6 + CON modifier (max +2 for this)

I can't recall offhand which level, but these classes have a specific level at which point they stop gaining HPs by roll and instead just get a set amount per level. I believe it's 3 for warriors (and I think this occurs at level 10 and thereafter), 2 for priest types and rogue classes (I believe this is at level 9 and thereafter) and 1 for mages (I think this is level 9 as well).

I also think there's a setting in the config file that will grant max HPs per level, but I could be thinking of IWD on this one.

It varies by class and level (only 1 hp per level at some higher levels) and, of course, a constitution boost, too.

If you want max hp, you should be able to set your difficulty to a medium or easy level to receive max HP -- then just move the difficulty up after you're done leveling. That'll be a lot faster than reloading a lot. (note: I've never tried that, but it should work - -someone correct me if I'm wrong)

It is a bit of a cheat to reload/change the difficulty to get max hp, though, and certainly isn't needed to win the game. You may well find it more enjoyable to actually play it as intended: the rolls will almost certainly average out over time, and you'll end up with somewhere near the middle of the amount of hp available.

Just a small tip: If you do this it would be easier to just lower the game's difficulty to easy before levelling up; that way characters will always get the maximum amount of HP based on their class+CON. After that you can change back to whatever difficulty you're playing on.

The biggest issue with this is a run of bad luck (which happens more often than one might think) where your character gets 1 HP on successive level-ups. While this isn't a big deal if it happens on one level-up, it can be HUGE if it happens two or three times in a row and you're at very low levels.

IMO, the first two or three levels should be max HPs on level up and then random after that. This seems to strike a good balance between survivability of the characters (and thus fun for the player), and avoiding cheesiness.

In BG1 Jaheira is a Fighter / Druid with 17 Constitution. For the first three levels, the maximum hit points is:

Average of 10 and 8, +3 = 12 hit points per level.

The fighter level is half of 10 + 3 or 6.5 hit points per level.
The druid level is half of 8 + 3 or 5.5 hit points per level.

If one class is leveled and not the other, then we are only getting half the constitution bonus. How is this rounded based on whether the sum of fighter and druid levels is even or odd?

The constitution bonus is a level up bonus, not a class bonus (though it does vary by class), so it applies ONCE per level up regardless of how many classes. So if Jaheira's both classes level up together, she will get (1 to 5) + (1 to 4) +3, if only her fighter levels she will get (1 to 5) +3, and only her druid will get (1 to 4) + 2. At least that's how I understand it.

I always thought that Neverwinter Nights' solution was a pretty good one. It was all random, but guaranteed to be in the top half of the roll for your class.

So if your hit dice is d6, you'd always get somewhere between 4-6 on level up.

BG2 Tweak Pack (not sure about BG1) can add that as an option.

Oh, I am SO going to do this! Cheat, cheese, whatever...getting a 1 HP increase is cheating ME, so I see no real reason to take the proverbial high road on this one! 8^)

Not sure if the Tweak Pack has that particular option, but I believe you can turn on max HPs at level up. Either way though, the AD&D rules can be brutal when it comes to lower level characters if they get very few HPs. A string of bad rolls just makes it no fun, so I wouldn't feel guilty about it.

Just tried it last night and even after setting my game at "easy" level, I got varied HP boosts at Level-Up, so I guess I'll just keep repeating until I get good boosts. No biggie as far as time consumption; I've already had to restart my main character and game multiple times due to being a noob and really screwing myself. That and a corrupted save-game after I'd hit Chapter 7. Fun fun.