Baldur's Gate 3 Dice Calculator

How Does the Formula Work?

The Baldur's Gate 3 Dice Calculator computes the exact probability of succeeding on any d20 roll in the game. Whether you face a persuasion check, a crucial attack roll, or a saving throw against a dragon's breath, this tool tells you your precise chances based on the Difficulty Class (DC), your total modifier, and whether you have advantage, disadvantage, or Elven Accuracy. Understanding these probabilities helps you make better tactical decisions about when to use resources like Inspiration, Guidance, or Bardic Inspiration.

How the D20 System Works

Baldur's Gate 3 faithfully implements the Dungeons and Dragons 5th Edition d20 system. Every skill check, attack roll, and saving throw follows the same core mechanic: roll a 20-sided die, add relevant modifiers, and compare the total to a target number called the Difficulty Class (DC). If your total meets or exceeds the DC, you succeed. The DC ranges from 5 (very easy) to 30 (nearly impossible). Your modifier combines your ability score modifier (typically -1 to +5), proficiency bonus (+2 to +6 based on level), and any additional bonuses from spells, items, or class features.

Advantage and Disadvantage

The advantage/disadvantage system is one of D&D 5e's most elegant mechanics. Advantage lets you roll the d20 twice and take the better result, dramatically improving your odds. On a DC 15 check with +3 modifier (needing 12 or higher), normal probability is 45%, but advantage raises it to 69.75%. Disadvantage does the opposite, taking the worse of two rolls: the same check drops to 20.25%. In BG3, many abilities grant advantage: attacking from stealth, the Help action, certain spells (Faerie Fire, Guiding Bolt), and high ground positioning. Sources of disadvantage include prone targets at range, poisoned condition, and low ground penalty.

Elven Accuracy

Elven Accuracy is a powerful feat exclusive to elves and half-elves. When you make an attack roll or ability check with advantage using Dexterity, Intelligence, Wisdom, or Charisma, you roll three d20s instead of two and take the highest. This effectively turns advantage into "super advantage." The probability jump is significant: a DC 15 check needing 12+ goes from 69.75% (regular advantage) to 78.4% (Elven Accuracy). The nat 20 chance jumps from 9.75% to 14.26%, making critical hits substantially more common. This feat is particularly devastating on builds focused on critical hits, such as Champion Fighter multiclass or Assassin Rogue.

Critical Hits and Misses

A natural 20 on an attack roll is always a critical hit, doubling all damage dice. In BG3, this is especially impactful with weapons that have multiple damage dice (like greatswords at 2d6) or when combined with Sneak Attack (adding up to 6d6 at higher levels). A natural 1 on an attack roll always misses, regardless of how high your modifier is. For skill checks and saving throws, BG3 treats natural 20 as automatic success and natural 1 as automatic failure, though this differs from strict D&D 5e rules where only attack rolls have these automatic results. The calculator shows your nat 20 and nat 1 chances for all roll modes.

Common DC Values in BG3

Understanding typical DC values helps plan your character build. Most dialogue skill checks in Act 1 range from DC 10 to DC 15. Lock picking DCs range from 10 (simple locks) to 20 (complex locks) to 30 (the hardest locks in the game). Spell saving throw DCs for enemies range from 12 to 18 in Act 1, climbing to 15-21 in Act 3. The final boss encounters feature DCs of 17-21. Your own spell save DC equals 8 + proficiency bonus + spellcasting ability modifier. A level 10 wizard with 20 Intelligence has DC 19, meaning enemies need to roll 19 or higher on their saving throws if they have no modifier.

Tactical Use of Probability

Knowing your exact success probability transforms how you play BG3. If a persuasion check has only a 25% chance of success, you might use Guidance (+1d4 average 2.5 to the roll) to boost it to 37.5%, or have a character with Enhance Ability cast on them for advantage, pushing it to 43.75%. Stacking these bonuses turns risky checks into probable successes. In combat, calculating whether your attack will likely hit determines whether to attack normally, use a resource for advantage, or switch to a spell with a saving throw that targets a weaker defense. The calculator lets you compare these scenarios side by side.