D&D 5e Advantage & Disadvantage Calculator
Calculate exact hit and success odds rolling 2d20 with Advantage (keep highest) or Disadvantage (keep lowest) against any Target Armor Class (AC) or DC.
⚙️ Input Parameters
Real-Time Simulation Advantage: P(Success) = 1 - (1 - p)^2 | Disadvantage: P(Success) = p^2 (where p = normal success probability) Tactical Analysis & Mathematical Context
In tabletop gaming, understanding the mathematical distribution behind your rolls allows you to make informed risk-reward decisions. Whether balancing spell slot usage in D&D 5e, evaluating an attack profile in Warhammer 40k, or weighing trade routes in Catan, knowing the exact probability mass function (PMF) turns guesswork into strategy.
Frequently Asked Questions
How much is Advantage worth in D&D 5e?
Advantage is mathematically equivalent to an average bonus of +3.325 to your roll across all target numbers. At target rolls around 11 (a 50% baseline chance), Advantage provides the maximum benefit of +5 (increasing success from 50% to 75%). Near extreme edges (needing a 2 or a 20), the effective bonus is smaller (+0.95).
What are the odds of rolling a Natural 20 with Advantage?
With standard roll, your chance of a Natural 20 is 1/20 (5.0%). With Advantage, rolling two d20s gives a 1 - (19/20)^2 = 9.75% chance of landing at least one Natural 20 (nearly double).
What are the odds of a Natural 1 with Disadvantage?
With Disadvantage, the probability of rolling at least one Natural 1 jumps from 5.0% to 9.75%.