Most bonuses come from a particular source; these modifiers will have an adjective to describe them, such as feat bonuses or class bonuses or circumstance bonuses or racial bonuses. Bonuses are always positive; if an effect would cause a bonus to be negative, treat it as zero instead.
If several bonuses apply to the roll you are about to make that all have the same adjective, only the highest one applies, and only once. For example, if you have a +2 class bonus to saving throws, and a +5 class bonus to saving throws vs. charm effects, then you apply the +5 modifier when making a saving throw vs. a charm effect, not the +7 that you would get from adding them together. However, if you have two different bonuses, such as a +5 class bonus and a +2 training bonus, you may add them both to the roll. Untyped bonuses are bonuses which have no type - you add all of these together when you make your roll.
Common Bonus Types
An Ability Bonus is the most common kind of bonus that you add to rolls and defenses. Your Ability bonus is equal to half of the sum of your level and your ability modifier, rounded down.
A Size Bonus is a bonus that you receive from your character's size. Size bonuses are usually static, unless something changes your character's size; that is, you apply them during character creation, and they are a permanent addition to your character unless something changes your size. Medium creatures receive no size bonus; small creatures receive a +1 size bonus to reflex and weapon attacks and a -1 size penalty to fortitude and melee damage; tiny creatures receive a +2 size bonus to reflex and weapon attacks and a -2 size penalty to fortitude and melee damage. Large creatures receive a +1 size bonus to fortitude and weapon damage and a -1 size penalty to weapon attacks and reflex; huge creatures receive a +2 size bonus to fortitude and weapon damage and a -2 size penalty to reflex and weapon attacks.
A Racial Bonus is a bonus that you receive from your character's race. Racial bonuses are almost always static; that is, you apply them during character creation, and they are a permanent addition to your character. Some racial bonuses come from racial feats, however, and some racial feats can even grant other characters a racial bonus. If you grant yourself or another character a racial bonus to a trait that they already have a racial bonus in, only the highest racial bonus applies to that trait for that character.
A Class Bonus is a bonus that you receive from your character class. Class bonuses are usually static; that is, you apply them during character creation, and they are a permanent addition to your character. Some class bonuses come from class feats, however, and some class features or class feats can even grant other characters a class bonus. If you grant yourself or another character a class bonus to a trait that they already have a class bonus in, only the highest class bonus applies to that trait for that character.
For each of your Proficiencies, your proficiency check modifier for that proficiency is equal to:
- the ability modifier for that proficiency if you are untrained.
- the ability modifier plus your training bonus if you are proficient.
- the ability modifier plus your training bonus plus your expertise bonus if you have expertise.
A Stance Bonus is a bonus that you receive from entering a stance. Stance bonuses last as long as you maintain that stance, and end as soon as you end that stance. A few non-stance feats grant you a stance bonus; while these feats do not place you in a stance, their bonuses work similarly enough to stance bonuses that they apply as such. If you somehow have two stance bonuses applying to the same trait, only the highest stance bonus applies to that trait.
A Feat Bonus is a bonus that you receive from performing a feat. Some feat bonuses have a duration - for example, a feat may specify that you gain a +2 feat bonus to speed until the end of your next turn. Other feat bonuses simply last for the duration of the feat itself - once you complete the feat's action, you no longer have the bonus. If you would apply multiple feat bonuses to the same trait, only the highest feat bonus applies to that trait.
An Equipment Bonus is a bonus that you receive from the equipment that you are using. There are several types of equipment bonuses.
Weapons and implements that permit attacks add their equipment bonus as an accuracy bonus to the attack roll. For example, a rapier's +3 to attack is an accuracy bonus.
A Circumstance Bonus is a bonus that you receive from the particular circumstances of your situation. Circumstance bonuses are usually due to environment, positioning, or a particularly clever use of available resources. Most of the time, if you ask your DM to do something interesting and clever, you will receive a circumstance bonus to the action based on how well he thinks your description of your efforts will add to the action you are attempting. If you could somehow apply multiple circumstance bonuses to the same trait, only the highest circumstance bonus applies to that trait.
When you have advantage against an opponent, all attacks that you perform against that opponent gain a +2 advantage bonus.
Melee Damage Bonus
Your melee damage bonus is equal to your Strength modifier unless modified by a class feature. When you make a basic melee attack, you add your melee damage bonus to the weapon's damage dice to determine the total damage dealt by the attack.
Ranged Damage Bonus
Your ranged damage bonus is equal to your Dexterity modifier unless modified by a class feature. When you make a basic ranged attack, you add your ranged damage bonus to the weapon's damage dice to determine the total damage dealt by the attack.
Magic Damage Bonus
Some characters can perform various kinds of divine magic. If your character can cast attack spells, trances, prayers, or other forms of damaging magic, those attacks will often add your magic damage bonus to the attack's damage dice roll. Your magic damage bonus is based on an ability score, but which score depends on the kind of magic you cast - Wizards use Intelligence, while Bards and Sorcerers use Charisma, and Barbarians and Priests often use Wisdom.
An important part of combat is using the environment to your advantage - terrain can offer you something to duck behind to avoid an attack. Anything solid that can physically deflect or stop an attack is cover. When you have cover, you gain a cover bonus to your armor, reflex and fortitude defenses based on the amount of cover available. This bonus can range from +1 for something flimsy or small like a young sapling, to +5 for hiding behind a solid steel door while peeking out occasionally to aim.
Depending on the layout of the battlefield, an object can provide cover against attacks from one direction but not another. For example, if your back is to a chest-high wall, you would receive cover from the wall for all attacks that come from the other side of that wall, but would not receive cover from attacks that originate from the same side of the wall as you.
In addition to terrain, shields also provide cover. A shield provides between a +1 and +5 cover bonus, depending on the size of the shield. Shields provide cover from all directions, because you are assumed to be maneuvering to position the shield between yourself and attacks. If you would receive cover from both a shield and terrain, only the highest cover bonus applies.
When you are concealed, you are hidden from view.
When you have partial concealment, creatures suffer a -2 penalty to spot you or perform ranged attacks against you, and you gain a +2 bonus to Stealth checks. It is possible to have partial concealment from some creatures and not others - for example, if you are standing next to a translucent rice-paper wall, you have partial concealment against creatures on the other side of the wall, but not against creatures on the same side of the wall as you.
When you have total concealment, creatures suffer a -5 penalty to spot you or perform any attacks against you, and you gain a +5 bonus to Stealth checks. It is possible to be hidden from some creatures and not others - for example, if you are in total darkness, you have total concealment from creatures that rely on normal vision to see, but not against creatures with darkvision.