How do you combine BABs for high level classes?

[MonkeySage]

The NPC I'm working on gets three attacks from its druid bab, two attacks from its ranger bab, and two attacks from outsider bab.

Looks like:
15/10/5
10/5
10/5

How do I combine these scores?

This is for the avatar of a deity, whom I intend to have spar with one of the players.

[BowStreetRunner]

So you are talking a level 20 druid, level 10 ranger, level 10 outsider? Is this a level 40 character? A level 20 gestalt character? Or something else?

[torrasque666]

The NPC I'm working on gets three attacks from its druid bab, two attacks from its ranger bab, and two attacks from outsider bab.

Looks like:
15/10/5
10/5
10/5

How do I combine these scores?

This is for the avatar of a deity, whom I intend to have spar with one of the players.
So its a Druid 20/Ranger 10/Outsider 10? For starters, you don't continue to gain BAB past ECL 20. So assuming that they hit Outsider 10/Druid 10 pre-epic, they'd have 17/12/7/2. And that's it. They gain Epic Attack Bonus past 20, but this does not grant additional attacks. Due to having 40 hitdie as a character (creatures have different rules. they never hit a cap on their BAB from RHD AFAICT) they have an additional +10 on their attack rolls, leading to 27/22/17/12 before other bonuses.

[MonkeySage]

Level 40; he's the avatar of a god. But, this is sort of a taste of what is ultimately intended to be an epic level campaign. The player who will fight him already kind of worships him, and the fight isn't to the death.

[eggynack]

You're overcomplicating it a bit. You don't have to meld together all the lower numbers, even if you can theoretically do it something like that. You just add the biggest numbers, and then add an extra attack at +6, +11, and +16, each time at a -5 compared to the next weakest attack. Epic rules do change things though, so you should check out the epic BAB rules.

[FearlessGnome]

The way BAB work once you pass level 20 is that you throw out the BAB for your class and just add 0.5 to attack. Or +1 for every two levels. So it's like everyone is a wizard. And you stop getting more attacks during your full attack.

So the result depends on the level order. If the character is a Druid20, Ranger10, Outside10, then they have three attacks on a full attack (except it's an Epic Druid, so they should be using spells or a Shapechange/Wildshape form that uses natural weapons.) If this is the leveling order, the BAB is 15/10/5, with +10 to all attacks.

Alternatively, if it's an Outsider10, Ranger10, Druid20, then the full attack is 20/15/10/5, with +10 to all attacks.

If it's Outsider10, Druid20, Ranger10, the full attack is 17/12/7/2, with +10 to all attacks.

Epic rules are not fantastic.

[Seppo87]

The basic rule is that you stack the highest BB from all classes and then determine the number of attacks.

Example:
Barbarian 6 + Fighter 6
You don't have to add 6/1 + 6/1,
just 6+6 = 12
with BaB 12, it naturally follows that it is 3 attacks: 12/7/2

Epic rules are a bit different though, as you do not gain actual BaB. You instead gain Epic Attack Bonus, which never grants additional attacks. Epic Attack Bonus is always 1 every 2 levels.

So, it's gonna require 2 steps:

1- Determine BaB
2- add half epic levels as Epic Attack Bonus

[DarkSoul]

It's the avatar of a deity; stack the levels to get as close to +20 by level 20 as you can. In your case, that means Outsider 10/Ranger 10. The 20 druid levels give a +10 Epic Attack Bonus.

Final result: +30/+25/+20/+15 BAB + EAB.

[BowStreetRunner]

It's the avatar of a deity; stack the levels to get as close to +20 by level 20 as you can. In your case, that means Outsider 10/Ranger 10. The 20 druid levels give a +10 Epic Attack Bonus.

Final result: +30/+25/+20/+15 BAB + EAB.
I'd agree that this is the best way to build it from the perspective of getting the highest BAB. Now whether there are other considerations to the order you apply your class levels is another matter.

[Jormengand]

I'd agree that this is the best way to build it from the perspective of getting the highest BAB. Now whether there are other considerations to the order you apply your class levels is another matter.

Highest HD first and most skill points first are usually the other ones, with skill points being more important because you get an extra 3 skill points for every one you'd normally get for a level in that class, whereas you only get half the HD difference as extra hit points. Either way, outsider is correct to take as the first level, then you can take the remaining outsider and ranger levels in any order, then the druid levels.

[BowStreetRunner]

...outsider is correct to take as the first level, then you can take the remaining outsider and ranger levels in any order, then the druid levels.
I was working under the assumption that all racial levels had to be taken before any class levels.

[Jormengand]

I was working under the assumption that all racial levels had to be taken before any class levels.

Usually, yes, but if you have an acquired template that gives you RHD, or if you gain divine ranks and weren't born with them, you may find yourself gaining extra RHD after you already have class levels. In any case, it doesn't matter whether you have to take them first or not, because you should be taking them first even if you don't have to.

[Âmesang]

As far as I'm aware becoming a deity doesn't grant you outsider HD unless you had some to begin with; granted, I'm basing this on Hercules, Imhotep, and Vecna from Deities and Demigods and Azuth, Bane, Cyric, Kelemvor, Midnight/Mystra, Torm, and Uthgar from Faiths and Pantheons.

EDIT: To try and explain further, I was under the impression that those deities who had 20 outsider HD were effectively "born" with them before taking class levels; although, last I checked, neither book mentioned what class skills they gain for their racial HD (and the Monster Manual is silent, since I believe it's intended to be dependent on creature, not creature-type), so I've always had natural-born deities treat all skills as class skills with regards to their racial HD.

[Durzan]

or, you know, you can just ignore the rules dealing with BAB at epic levels. For me, epic levels function just like normal leveling... just once you max out a class, you must start taking levels in a different class. BAB, Saves, etc. Don't change in how they operate... although I will not let someone have more than 4 natural attacks in a full attack round (With exceptions of class abilities like Flurry of Blows).