Dice rolls
Attacking a creature, making a shove attempt, spotting a hidden secret, and picking a lock are all examples of die rolls, which are the main method used to determine character success or failure in BG3. The amount of damage a character deals in combat is also determined by rolling dice.
In most circumstances, when a character makes a die roll, their Ability Score Modifier and Proficiency Bonus are added to the roll to determine the final result. The most common exception to this is the Damage Roll, which doesn't add a character's proficiency bonus unless explicitly stated.
The various types of dice used in rolls are referred to by the number of sides they have: 
D4, 
D6, 
D8, 
D10, 
D12, and 
d20. Abbreviations are used to refer to the total number of dice used in a roll, such as 1d6 for rolling one D6 die, 2d4 for rolling two D4 dice, 8d6 for rolling eight D6 dice, and so on.
Some rolls need to reach a certain value to be considered a success. This is usually done with a d20, and the target value is called the Difficulty Class of the roll. Rolling a 1 on a D20 is referred to as a Natural 1 and rolling a 20 is referred to as a Natural 20. On some rolls, these can have special effects, such as automatically failing or succeeding the roll, ignoring Modifiers and Difficulty Class.
Karmic Dice
When the Karmic Dice option is enabled (the default), the game will avoid frustrating streaks of very low rolls in a row.
However, Karmic Dice influence all rolls – including those of enemies – and the results will only ever skew toward a positive result for the dice roller. In short, the Karmic Dice setting makes combat encounters quicker and deadlier for both you and your enemies.
The exact algorithm for Karmic Dice is not presently known and may be changed between versions of the game.
Karmic Dice was previously referred to as 'Loaded Dice'.
Types of Rolls
There are four main kinds of rolls in the game, each with their own specific variations on the general rules above. Attack Rolls, Saving Throws and Ability Checks all use a d20; other types of dice are mostly used for Damage Rolls. Initiative is an exception.
Attack Roll
Main page: Attack Roll
When a creature attacks another, the game rolls a D20. The die result is modified by the attacking creature's Ability Score Modifier and Proficiency Bonus. If the result matches or exceeds the Armour Class of the target, then the attack is successful. Otherwise, it's a failure; this could mean the attack was a miss, failed to hurt the target due to its armour, or the target was able to dodge or parry.
d20 + Ability Score Modifier + Proficiency BonusAttacks made with Weapons always use an Attack Roll to determine success. Some spells also use an Attack Roll, usually those that involve magical beams or projectiles that need to be aimed at a target (such as 
or 
). Creatures or objects conjured by spells (such as 
Flaming Sphere) can often attack on their own turns, and make an Attack Roll to do so.
Spells which directly affect a target (such as 
) or which cause an effect at a point in space (such as 
or 
) don't require an Attack Roll, but usually allow affected creatures to make a Saving Throw instead (see below).
A successful Attack Roll results in a separate Damage Roll to determine the amount of damage done to the target.
Critical Miss / Critical Hit
As a special case, a roll of 1 means that the attack fails regardless of bonuses or the target's Armour Class. This is called a Critical Miss.
Likewise, a roll of 20 means the attack succeeds regardless of the target's Armour Class. This is called a Critical Hit. A critical hit also affects the result of the Damage Roll: it doubles the normal number of damage dice rolled (including additional dice such as those from Smites or Combat Manoeuvers). Flat damage bonuses from modifiers or other sources (such as 
) are not affected by a critical hit.
Attack Roll Modifiers
The Ability Score Modifier used for an Attack Roll depends on the type of attack being made. Melee and ranged weapon attacks use Strength or Dexterity, depending on the weapon. Spells use a specific Spellcasting Ability Modifier usually determined by the caster's class; see the main Attack Roll page for details.
A creature's Proficiency Bonus is added to the roll if it is proficient in the specific kind of attack it's making. For weapon attacks, this means having proficiency in the weapon used. For spells, it's based on whether the creature has any innate spell casting capability granted by its class, subclass, or Feats.
Attack Rolls can also have 
Advantage / 
Disadvantage.
Damage Roll
Main page: Damage Roll
A Damage Roll is made when an attack is successful, a spell hits a target, a trap is activated, and so on. The result determines the damage dealt to an affected creature or object, measured in Hit Points. This roll can involve any size and number of dice, determined by the source of the damage. The dice expression is written "ndx + m", where n is the number of dice, x is the size of the dice rolled, and m is the total of any modifiers that apply (see below). The results of multiple dice are added together. Damage rolls also have a Damage Type.
For example, a Dagger uses a single D4 for Damage Rolls, and deals Piercing Damage. Assuming no modifiers apply, the game expresses this as "1d4 (1-4) damage - 
Piercing", with "(1-4)" being the range of possible damage values. Most weapons use a single die, though a Greatsword deals 2d6 slashing damage. Being caught in a will cause 8d6 points of fire damage, though a successful Saving Throw (see below) can reduce it to half.
Damage Roll Modifiers
Attacks made with weapons always add the attacking creature's Ability Score Modifier, generally Strength or Dexterity (whichever was used for the Attack Roll). Spell attacks generally do not add such a modifier, except when explicitly granted by a magical item or class feature, such as the Warlock's 
invocation. Some magical affects, like the spell 
, allow spellcasters to use their Spellcasting Ability Modifier for weapon Attack and Damage Rolls.
Saving Throw
Main page: Saving Throw
Various types of danger can be avoided, or their harm reduced, by making a 
Saving throw, or "save" for short. This could mean dodging a dart or burst of flame from a sprung trap, resisting the effects of poisons or mind-altering magic, or trying to take cover to reduce damage from an explosion.
The creature rolls a D20, and adds its Ability Score Modifier and Proficiency Bonus (if Proficient in that type of saving throw). The result must equal or exceed the Difficulty Class of the Saving Throw.
d20 + Ability Score Modifier + Proficiency Bonus (if Proficient)Saving Throw Modifiers
The Ability Score Modifier used for a save is determined by the source of danger. For example, evading a spike trap may require Dexterity, whereas trying to resist the effects of a poisonous gas would require Constitution. They are usually referred to by the Ability used, for example "Strength Saving Throw" or "Strength Save". Dexterity, Constitution and Wisdom Saving Throws are much more common than Strength, Intelligence or Charisma Saves.
The Proficiency Bonus is only added if the creature has Proficiency in the corresponding type of Saving Throw. This is generally granted by a creature's Class, each of which comes with two Saving Throw Proficiencies.
Some magical effects and items may also grant bonuses to Saving Throws.
Difficulty Class
The Difficulty Class (DC) is a number that must be matched or exceeded to achieve success when rolling for Ability Checks or Saving Throws. (Attack Rolls use the target's Armour Class instead.) The Difficulty Class (DC) is determined by the source of danger:
- In scenarios such as traps or conversation events, the game chooses an appropriate Difficulty Class, depending on how serious the danger is.
- Spells that impose Saving Throws have a DC determined by the creature's Spellcasting Ability Modifier, using the following formula:
- For the Difficulty Class of a Weapon Action that imposes a Saving Throw, the DC is determined by the creature's Dexterity or Strength - whichever is higher - and a Weapon Ability's inherent DC Bonus, using the following formula:
Effect of Success
A successful Save can mean completely avoiding negative effects, reducing the damage received (usually by half), or both. For example, successfully saving against a spike trap could mean that a creature takes no damage at all, because it successfully evaded the spikes. On the other hand, if it's caught in the area of effect of a , then a successful save will merely halve the damage. Saving against 
both halves the damage taken, and prevents a creature from being pushed by the spell.
Some effects don't allow for a Saving Throw at all, for example the spell 
.
Ability Check
Main page: Ability Check
Various actions, other than attacking or making a save, still require the creature to make an attempt that may fail. The creature rolls a D20, and adds its Ability Score Modifier and possibly its Proficiency Bonus. The attempted action has a specific Difficulty Class which the result of the roll must match or exceed.
d20 + Ability Score Modifier + Proficiency BonusSome Ability Checks are based only on the base Ability Score. A common example is exerting willpower to use the Tadpole's influence on other characters during dialogue. Checks like this have no applicable proficiency, and never add a proficiency bonus.
Skill Check
Most Ability Checks are tasks related to a specific Skill, also known as Skill Checks. Each Skill is associated with a specific Ability Score, and lets the creature add its Proficiency Bonus to the check if they are Proficient in that Skill. Some class features may grant Expertise, which doubles the Proficiency Bonus for one or more specific Skills.
Some Skill Checks are instigated by the player, while others are automatically triggered in response to other player actions. For example, when a character nears an unactivated trap, the game rolls a Perception Skill Check (or in short, "rolls Perception") to determine whether they notice it. Perception is a Wisdom Skill, so the character adds their Wisdom Modifier and, if proficient in Perception, their Proficiency Bonus. Once the trap is seen, the character can interact with it to attempt to Disarm it, which requires a successful Sleight of Hand Check, a Dexterity Skill.
Skill Checks are also common during dialogue, where some responses require a Skill Check to determine the outcome. Examples include using Charisma-based Skills like Persuasion, Deception or Intimidation to influence others, or Intelligence-based Skills like Investigation, History or Religion to determine or remember facts.
Contest
A Contest is a special type of Ability Check in which two creatures both roll an Ability Check or Skill Check to oppose each other, and one wins over the other. The creatures don't necessarily roll the same type of check.
An example of this is the 
action. The creature attempting the Shove rolls Athletics, and the defending creature rolls either Athletics or Acrobatics (the game chooses the Skill with the highest bonus) to contest the Shove. If the attacker's roll is higher than the defender's, the Shove succeeds; otherwise it fails.
Initiative
Main page: Initiative
When combat starts, all combatants make an Initiative roll to determine the turn order. This is effectively a Dexterity Ability Check, but made using a D4 instead of a d20. Proficiency does not normally apply, but some class features, spells and magical items can provide bonuses to the Initiative roll.
Advantage / Disadvantage
Main page: Advantage
In various situations, a creature can have Advantage or Disadvantage on an Attack Roll, Saving Throw, or Ability Check.
Advantage means that you make the roll twice and use the higher result. Disadvantage means you use the lower result.
Advantage and Disadvantage cannot stack. In other words, you never roll more than twice. Additionally, they cancel each other out, no matter how many sources of Advantage or Disadvantage you have. For instance, if you had three sources of Advantage and only one source of Disadvantage, they would still cancel each other out, causing you to roll normally.
