An attack roll represents your attempt to strike your opponent on your turn in a round. When you make an attack roll, you roll a d20 and add your attack bonus. (Other modifiers may also apply to this roll.)
If your result equals or beats the target's Defence, you hit and deal damage.
When NPCs attack you, you make a Defence Roll against their Attack DC - see Defence bonus, below.
Each creature has a base attack bonus (BAB) which represents its skill in combat. As a character gains levels or Hit Dice, his base attack bonus improves. When a creature's base attack bonus reaches +6, he receives an additional attack in combat when he takes a full-attack action (which is one type of full-round action — see Combat).
Additional modifiers are added to this base attack bonus, depending on your ability scores and skill with a weapon - see Attack bonuses, below.
Your attack bonus with a melee weapon is the following:
* Base attack bonus + Strength modifier + size modifier
With a ranged weapon, your attack bonus is the following:
* Base attack bonus + Dexterity modifier + size modifier + range penalty
You may also add bonuses from class feats (like Weapon Focus), racial abilities (like the dwarf's racial bonus against giants), and circumstances (such as shooting a ranged weapon into melee).
A combat manoeuvre attack is an action taken in combat that does not directly cause harm to your opponent, such as attempting to trip him, disarm him, or grapple with him (see Combat).
Combat Manoeuvre Attack (CMA): This value represents how skilled a creature is at performing a combat manoeuvre. When attempting to perform a combat manoeuvre, this value is added to the character's d20 roll. It is made up of the character’s Base Attack Bonus, plus their Strength modifier, and any special size modifiers.
* CMA = BAB + Strength modifier + size modifier
Your Defence bonus is the following:
* Armour bonus (if any) + shield bonus (if any) + heroic bonus (if any) + Dexterity modifier + other modifiers
Armour and shield bonuses are found in Table: Armour and Shields in the Equipment section.
Your heroic bonus is the same your base attack bonus from your heroic class. (NPCs usually don't have heroic class levels, so they don't get a heroic bonus to defence.)
Note that armour limits your Dexterity bonus, so if you're wearing armour, you might not be able to apply your whole Dexterity bonus to your Defence (see Table: Armour and Shields in the Equipment section).
Sometimes you can't use your Dexterity bonus (if you have one). If you can't react to a blow, you can't use your Dexterity bonus to Defence. If you don't have a Dexterity bonus, your Defence does not change.
Your combat manoeuvre defence (CMD) score represents how hard it is to perform a combat manoeuvre attack against you. A creature's CMD is used as the difficulty class when performing a manoeuvre against that creature. It is made up of the creature’s Base Attack Bonus, plus their Strength and Dexterity modifiers, and any special size modifiers.
At the start of a battle, each combatant makes an initiative check. An initiative check is a Dexterity check. Each character applies his or her Dexterity modifier to the roll, as well as other modifiers from feats, spells, and other effects.
* Initiative = 1d20 + Dex modifier + special bonuses
If two or more combatants have the same initiative check result, the combatants who are tied act in order of total initiative modifier (highest first). If there is still a tie, the tied characters should roll to determine which one of them goes before the other.
Like an attack roll, a saving throw is a d20 roll plus a bonus based on your class and level (see Classes), and an associated ability score. Your saving throw modifier is:
* Base save bonus + ability modifier
Saving Throw Types
The three different kinds of saving throws are Fortitude, Reflex, and Will:
Fortitude: These saves measure your ability to stand up to physical punishment or attacks against your vitality and health.
Apply your Constitution modifier to your Fortitude saving throws.
Reflex: These saves test your ability to dodge area attacks and unexpected situations.
Apply your Dexterity modifier to your Reflex saving throws.
Will: These saves reflect your resistance to mental influence as well as many magical effects.
Apply your Wisdom modifier to your Will saving throws.