Advantage. If you have Advantage on a D20 Test, roll two d20s, and use the higher roll. A roll can’t be affected by more than one Advantage, and Advantage and Disadvantage on the same roll cancel each other.
Disadvantage. If you have Disadvantage on a D20 Test, roll two d20s and use the lower roll. A roll can’t be affected by more than one Disadvantage, and Advantage and Disadvantage on the same roll cancel each other.
D20 Tests. When the outcome of an action is uncertain, the game uses a d20 roll to determine success or failure. These rolls are called D20 Tests, and they come in three kinds: ability checks, saving throws, and attack rolls. Roll 1d20; if the roll has Advantage or Disadvantage, you roll two d20s, but you use the number from only one of them—the higher one if you have Advantage or the lower one if you have Disadvantage. Then add the relevant ability modifier, your Proficiency Bonus if relevant, and any circumstantial bonuses and penalties, and compare the total to the target number. The target number for an ability check or a saving throw is called a Difficulty Class (DC). The target number for an attack roll is called an Armor Class (AC).
Interactions with Rerolls. When you have Advantage or Disadvantage and something in the game lets you reroll or replace the d20, you can reroll or replace only one die, not both. You choose which one. For example, if you have Heroic Inspiration and roll a 3 and an 18 on an ability check that has Advantage or Disadvantage, you could expend your Heroic Inspiration to reroll one of those dice, not both of them.
SRD 5.2.1 · CC BY 4.0