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Hit Probability Calculator

Enter accuracy and evasion to find your chance to hit.

How it is calculated

Accuracy, evasion, floor and cap are all read as percentage points. The raw chance is the plain difference raw = accuracy − evasion. It is then clamped: hit = max(floor, min(cap, raw)), so it can never fall below the floor or rise above the cap. Miss chance is 100 − hit, and the expected hits are hit ÷ 10 out of 10 attacks, shown with two decimals. The tool refuses a floor below 0, a cap above 100 or a floor higher than the cap. It models a single roll of this simple subtraction rule; games that use ratios, dice pools or multiple rolls need a different formula.

Worked example

Accuracy 90, evasion 30, floor 5 and cap 95. Raw chance: 90 − 30 = 60. Clamp: 60 is between 5 and 95, so it stays. Hit chance 60.0%, miss chance 100 − 60 = 40.0%, and 60 ÷ 10 = 6.00 expected hits out of 10 attacks. If accuracy were 110 against evasion 10, the raw 100 would be cut to the cap of 95, and with accuracy 20 against evasion 60 the raw −40 would be lifted to the floor of 5.

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Common mistakes

  • Entering a decimal such as 0.9 for 90 percent: the fields expect percentage points, so 0.9 would be read as under one percent.
  • Expecting a game that scales accuracy against evasion by a ratio to match: this tool subtracts evasion from accuracy, so it only fits systems that work that way.
  • Swapping floor and cap: a floor higher than the cap makes the tool return no result.
  • Forgetting the clamp: with accuracy well above evasion the raw number may exceed 100, but the displayed chance stops at the cap you set.
  • Reading the expected hits as a guarantee: 6.00 out of 10 is an average over many attacks, and any single run of 10 attacks can differ.

About this calculator

In tabletop and video game combat systems, the chance that an attack lands is usually modeled as the attacker’s accuracy stat working against the defender’s evasion stat, with the raw difference converted into a probability and then clamped between a floor and a cap — for instance never letting hit chance drop below 5% or exceed 95% — so that even heavily mismatched characters retain some chance of a hit or a miss, keeping outcomes unpredictable rather than deterministic.

Game designers tune these floors, caps and the accuracy-versus-evasion curve during balancing passes to control how punishing high evasion builds feel and how reliable high-accuracy builds are, since a formula with no clamping can make some matchups feel either guaranteed or hopeless.

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