Proficiency bonus
For a comprehensive summary of the mechanics behind all rolls and modifiers, see Die Rolls.
The Proficiency Bonus is a modifier applied to various Die Rolls based on the Level of a creature. It can affect Attack Rolls, Saving Throws, and Skill Checks, if the creature has the correct type of Proficiency for the situation. It doesn't apply to Damage Rolls.
When it's applied
Attack Roll
For [[Attack Roll]s using a Weapon, the creature must have Proficiency with the weapon it's using to make the attack.
For example, since a Fighter has Proficiency in all Simple Weapons and Martial Weapons, the Proficiency Bonus will be added to all melee and ranged weapon attacks.
On the other hand, a Wizard normally only has Proficiency in Daggers, Quarterstaves, and Light Crossbows, so the Proficiency Bonus won't be added to attacks made with any other weapon, unless the Wizard has Proficiency in that weapon for some other reason.
For spells that require an Attack Roll to hit, the Proficiency Bonus is added if the creature has the innate ability to cast spells. I.e., not just with items and scrolls. This means that, at higher levels (where the Proficiency Bonus starts making a significant difference), it's better to let spell casters use items and scrolls to cast spells.
Saving Throw
Saving Throws are categorized by Ability Score, such as Strength Saving Throw, Dexterity Saving Throw, and so on. For the Proficiency Bonus to be applied to a Saving Throw, the creature must have Proficiency in the corresponding type of Saving Throw. Each Class provides two Saving Throw Proficiencies. For example, the Fighter has Proficiency in Strength and Constitution Saving Throws, whereas the Wizard has Proficiency in Intelligence and Wisdom Saving Throws.
Skill Check
An Ability Check that's based on a Skill such as Athletics, Perception, or Sleight of Hand, is called a Skill Check. If a creature has Proficiency in the corresponding Skill, its Proficiency Bonus will be added to the roll.
Value
Following is the value of the Proficiency Bonus, based on the Level of the creature making the roll:
| Level | Proficiency Bonus |
|---|---|
| 1 to 4 | + 2 |
| 5 to 8 | + 3 |
| 9 to 12 | + 4 |