A character’s Base Attack Bonus is pretty self-explanatory: It’s the total Attack Bonus they’ve received from leveling up in various classes. Other factors will go on to modify this role in combat, including weapon choice, feats, bonuses from magical weapons and items, the use of various abilities, ability score modifiers and circumstance bonuses (flanking, invisibility, etc.) and spell buffs.

While a lot of things go into your Attack Bonus to arrive at the final score, the Base Attack Bonus is a relatively simple matter of tallying up the bonuses gained from your class levels. As with Saving Throws there are only a few different rates of progression: High Base Attack Bonus (warriors), Medium Base Attack Bonus (clerics, rogues) and Low Base Attack Bonus (arcane spellcasters).

Base Attack Bonus by Level¶

Not only does your Base Attack Bonus play a significant role in determining your Attack Rolls (and hence your prowess in combat), but once your Base Attack Bonus hits +6 you’ll gain a second attack, albeit at a +1 bonus. You continue to gain extra attacks as your Base Attack Bonus rises; three attacks when your Base Attack Bonus is +11 (+11/+6/+1), ultimately up to a maximum of four attacks when your Base Attack Bonus is +16 (+16/+11/+6/+1).

You must attack as a Full-Round Action to make use of your multiple attacks and, as noted above, each subsequent attack is made with a Base Attack Bonus five points lower. For example, a 6th-Level Fighter has a Base Attack Bonus of +6/+1; their primary attack has a +6 Base Attack, while their second attack receives a +1 Base Attack Bonus. A character’s Base Attack Bonus, then, is one of the primary factors that determines how well that character will perform in combat, with primary combatants (typically warriors) gaining a higher Base Attack Bonus, more attacks per round overall, and they’ll also gain these extra attacks quicker.