Attacks

An Attack Roll happens when the game wants to decide whether an attack will hit its target. The Attack Roll uses a D20 and can be affected by Modifiers such as the Ability Score Modifier and Proficiency Bonus of the creature making the attack.

Result = d20 + Ability Score Modifier + (optional) Proficiency Bonus

The result of the roll is compared to the Armour Class of the target. If the Armour Class is reached or exceeded, the attack is a successful hit, and the game proceeds with a Damage Roll to determine the amount of damage dealt.

Attacks done with Weapons always use an Attack Roll to determine success. Some spells also use an Attack Roll to determine whether they hit their intended target (such as Fire Bolt or Eldritch Blast), though other spells hit the target automatically (such as Magic Missile or Fireball). A spell that hits its target automatically may allow the target to make a Saving Throw instead.

Critical Miss / Critical Hit

Example of a Critical Hit with a 1d6 Shortsword. Notice how 2 d6 dice were used in the damage roll.

There are two special cases that needs to be considered. An attack roll of 1 means that the attack fails to connect, regardless of bonuses or the target's Armour Class. This is called a Critical Miss.

Likewise, an attack roll of 20 means the attack succeeds regardless of the target's Armour Class. This is called a Critical Hit. Additionally, the Damage Roll associated with a critical hit uses double the normal amount of all damage dice involved, this includes damage dice from additional sources such as sneak attacks, poison, and Paladin smites.

Certain Feats, Subclass feature, and Items can reduce the attack roll threshold of a critical hit by 1. These stack with one another making it possible for a creature to score a critical hit with an attack roll of 18 or even lower.

A few conditions also make it so that a critical hit is guaranteed under certain circumstances. Sleeping and Paralysed being the main examples.

Modifiers

Attack Rolls can be affected by Advantage/ Disadvantage, by the attacker's Ability Score Modifier, the attacker's Proficiency Bonus, Weapon Enchantments, Bless, High Ground/Low Ground, Bane, Loviatar's Blessing, Magic Weapon, Sacred Weapon, and Archery Fighting Style.

Ability Score Modifier

A bonus or penalty may be applied to the result of the roll based on an Ability Score. Which ability is used depends on the type of attack being made.

Weapons

Melee and ranged weapon attacks use Strength or Dexterity, depending on the weapon: usually Strength for melee weapons and Dexterity for ranged weapons. The exceptions to this rule are Finesse weapons, which automatically select Strength or Dexterity, whichever score is higher; and Thrown weapons, which use Strength for both melee and ranged attacks. If a weapon is both Thrown and Finesse, it uses the higher of Strength and Dexterity for both melee and ranged attacks.

Some examples, to make the possible combinations of Finesse and Thrown easier to understand:

Using a Maul for a melee attack always uses Strength.
Using a Rapier (Finesse) for a melee attack uses Strength or Dexterity; whichever the attacking creature has a higher score in.
Shooting a Longbow for a ranged attack always uses Dexterity.
Throwing a Handaxe (Thrown) for a ranged attack uses Strength.
Throwing a Dagger (Finesse & Thrown) for a ranged attack uses Strength or Dexterity, whichever is higher.

Spells

For spells, the Ability Score used for the Modifier depends on the class of the caster:

Classes sorted by which Ability Score they use for Spellcasting
Intelligence	Wisdom	Charisma
Wizard Arcane Trickster Eldritch Knight	Cleric Druid Ranger	Bard Paladin Sorcerer Warlock Barbarian (Scrolls only)

In Baldur's Gate 3, the same ability modifiers apply when casting a spell from a Scroll, even when the spell being cast is not normally available to your class. For instance, a Sorcerer casting Guiding Bolt (a Cleric-only spell) from a scroll adds its Charisma modifier to the Attack Roll of the spell.

Value of the Modifier

Whichever Ability Score ends up being used, the bonus or penalty value is based on this table, depending on how high the used Ability Score is:

Ability score modifier chart
Ability score	Modifier value	Ability score	Modifier value
1	-5	16-17	+3
2-3	-4	18-19	+4
4-5	-3	20-21	+5
6-7	-2	22-23	+6
8-9	-1	24-25	+7
10-11	+0	26-27	+8
12-13	+1	28-29	+9
14-15	+2	30	+10

Proficiency Bonus

The attacking creature's Proficiency Bonus is added to the result of the roll if the creature has the correct kind of Proficiency for the attack it's making.

For weapon attacks, the creature must have proficiency in the weapon it's using to make the attack.

For spell attacks, the creature must have innate spell casting capabilities granted by its Class, Subclass, or Feats. As a notable exception, despite not being able to cast spells normally, Barbarians receive their Proficiency Bonus when casting spells from Scrolls (as of Early Access Patch 9).

The value of the bonus depends on the attacking creature's Level:

Proficiency Bonus Chart
Level	Proficiency Bonus
1 to 4	+ 2
5 to 8	+ 3
9 to 12	+ 4

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