🐉 Combat Engine
D&D 5e Attack Hit Probability Calculator
Calculate exact hit, miss, and critical hit percentage given your Attack Bonus and the target Armor Class (AC).
⚙️ Input Parameters
Real-Time Simulation 7
-2 20
16
5 30
Mathematical Formula
Target Roll = AC - AttackBonus; P(Hit) = clamp((21 - TargetRoll)/20, 0.05, 0.95)
Primary Probability Result
--%
Success Probability
Fractional Odds
1 in 2.0
Failure Chance
50.0%
Client-side mathematical calculation ● 100% Deterministic
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
Does a Natural 20 always hit in D&D 5e?
Yes, an unmodified roll of 20 on the d20 is an automatic hit regardless of the target Armor Class, and is also a critical hit. Conversely, a Natural 1 is an automatic miss.
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