Fractional Base Bonuses
Each of the classes has an incremental progression for their Base Attack Bonus and saving throws. BAB rises by 1, ¾, or ½ per level. Good saves rise by ½ per level, while poor saves rise by 1/3. The general rule in Pathfinder is to round down. The Core Rulebook deals with this math by doing it for you. Your first level wizard’s BAB is +0 in the entry but, mathematically, it’s actually ½. This isn’t a problem when a character plays the same class as she progresses in levels.
However, it’s a huge disincentive to multiclassing. It’s also a disincentive to taking prestige classes. A cleric’s BAB increases by ¾ every level. A wizard’s rises by only ½. Under the traditional system, a multiclassing character takes the bonuses granted by her two classes and adds them together. So, a cleric 1/wizard 1 character takes her cleric BAB (3/4) and rounds it down to 0. The wizard BAB is also rounded down to 0. So, a second-level character has a BAB of +0 under this system.
Fixing Base Attack Bonus
Pathfinder Unchained tries to solve this problem by exposing the underlying math. Rather than rounding and then adding, you add and then you round. So, our PC’s BAB is ¾ + ½ or 1¼. Now, we round that number down and, voila!, the wizard 1/cleric 1 character has a +1 BAB. The character is no longer penalized for deciding to multiclass. Rather, the character is gaining skills just as a member of her class ought to.
Iterative attacks are also easily dealt with—when a character reaches +6, +11, +16, or +21 BAB, she gains another attack. Assuming she takes alternating levels in cleric and wizard, our cleric 1/wizard 1 will gain her second attack at cleric 5/wizard 5 with a BAB just over +6. A cleric gains her second attack at 8th level. It takes a wizard until 12th level. Lo and behold! The average of the two is when the second iterative attack occurs, just as common sense suggests it ought to.
Under the traditional rules, saving throws are also a little bit wonky when a PC decides to multiclass. PCs begin the game with a +2 bonus to their good saving throws, which rise at ½ per level (so, a 1st level character’s good save is actually +2½). There are two real problems here. First, under the traditional rules, a character could take a level dip into a class that has her initial class’ bad saves as good saves and effectively get a +2 bonus. Because the system advances poor saves at +1/3 per level, that’s effectively granting a six level bonus!
Alternately, a character could take a level dip into another class that shares a strong save with her initial class and tack an extra +2 onto her character’s good save—essentially granting 4 levels of good save progression with a single level dip. This is why many GMs house rule against giving multiclassed characters the extra +2 from their new class’ good saves—which feels fair but also removes one of the few rationales to take a level dip under the traditional rules.
Fractional Base Statistics compensates for this issue as well. PCs still get the +2 bonus to their initial class’ good saves. But, after that, it’s all based on fractional progression. Then the system operates the same way as it does for BAB. The different class’ bonuses are added together and then rounded down. Taking a level in a new class doesn’t grant the extra +2 bonus, which feels fair.
Overall, I like the Fractional Base Bonuses system. It’s a little more complex than the traditional system, but I don’t think that’s a problem that overshadows its usefulness. First of all, beginning characters are the ones most likely to be confused by the math in the game. But, beginning characters aren’t likely to want to play multiclassed characters anyway—some of them won’t even realize the option is available. The math can be a little complicated, but the table on p. 41 means that calculating new BAB and saving throws requires little more than the ability to add up fractions with bases quarters, halves and (not technically fractions) whole numbers. That’s not a heavy lift. The fractional BAB system works well and the saving throw system compensates for some strange results that multiclassing under the traditional system. On balance, it’s a tiny bit more complicated in exchange for incredibly superior results. Fractional Bases Bonuses, welcome to my table. You’re in!