Base attack bonus

Base attack bonus (BAB) is an attack bonus derived from the character's class levels.

Each level taken in a class increases the total BAB of a character by a certain amount.

The base attack bonus increase occurs at different rates for different character classes.

Additional attacks
A character gains a second attack per round when his or her base attack bonus reaches +6, a third with a base attack bonus of +11 or higher, and a fourth with a base attack bonus of +16 or higher.

When an additional attack is gained the attack bonus for this attack is 5 points lower than the previous lowest attack.

Any other modifiers on attack rolls apply to all these attacks normally, but bonuses do not grant extra attacks.

e.g.

A character with +6 BAB has one attack at +6 and a second attack at +1. When this character reaches +11 BAB, this second attack has reached +6 and gains a 3rd attack with +1.

Notation
If a character has multiple attacks this is written with the highest AB (the actual BAB) first with a / used to seperate each additional attack's bonus.

e.g.

A character with +18 BAB has 4 attacks at +18/+13/+8/+3

Class BABs
Classes are divided into 3 groups based on how their BAB progresses. Those who are more capable warriors fall into the "high" group.

Multiclassing
When a character multiclasses each class provides seperate BAB progressions. Even if the BAB each class provides is of the same type the progressions do not follow on.

e.g.

A level 20 rogue (average BAB) has a +15 BAB, while a character with 10 rogue levels and 10 monk (also average BAB) levels would gain +7 BAB from each class, to a total of +14 BAB.

Base attack bonus progression
* a character with only a single class, with this BAB progression, gains an additional attack at this point.