D&D Roll Odds Calculator

About this calculator

This calculator finds the probability of meeting or beating a Difficulty Class (DC) when rolling a d20 in Dungeons & Dragons 5th edition, under three roll types: a normal single roll, rolling with advantage (roll two d20s, keep the higher), and rolling with disadvantage (roll two d20s, keep the lower). Advantage and disadvantage don't shift the odds linearly — they skew the probability distribution toward high or low results, with the biggest swing happening for DCs near the middle of the range.

Players and Dungeon Masters use it to understand how big an edge advantage really gives (often described loosely as "+5", though the actual bonus varies by DC) and to balance encounters and skill checks fairly. Enter your modifier and target DC to see your hit chance under normal, advantage, and disadvantage rolls.