TUTORIAL: Damage formulas 101

RPGツクール 素材
1

Damage Formulas 101
A comprehensive guide for RPG Maker MV & MZ

Damage formulas in RPG Maker are plain JavaScript expressions.
They follow normal math order of operations (PEMDAS):

  1. Parentheses
  2. Exponents
  3. Multiplication & Division (left to right)
  4. Addition & Subtraction (left to right)

Because of this, a.atk * 4 - b.def * 2 is not the same as (a.atk * 4 - b.def) * 2.
Always use parentheses when you need to control the order.

The Two Most Important Variables

a = the user (attacker)
b = the target (defender)

You can access almost any parameter from them:

a.atk, a.def, a.mat, a.mdf, a.agi, a.luk
a.hp, a.mp, a.tp, a.mhp, a.mmp
a.level, a.hpRate(), a.mpRate(), a.tpRate()

Same options exist for b.

Basic Operators

  • Addition → a.atk + 50

  • Subtraction → a.atk - b.def

  • Multiplication → a.atk * 4
    / Division → a.atk / 2
    % Modulo → a.hp % 10
    ** Exponent → a.atk ** 2

Useful Math Functions

Math.max(x, y) // higher value
Math.min(x, y) // lower value
Math.floor(x) // round down
Math.ceil(x) // round up
Math.round(x) // normal rounding
Math.random() // 0 to 1
Math.randomInt(n) // 0 to n-1

Essential Formula Building Blocks

  1. Classic Physical
    a.atk * 4 - b.def * 2

  2. Classic Magical
    a.mat * 4 - b.mdf * 2

  3. Percentage of Max HP
    b.mhp * 0.25

  4. Current / Missing HP
    b.hp * 0.3
    (b.mhp - b.hp) * 0.5

  5. Level Scaling
    a.atk * 2 + a.level * 5

  6. Minimum Damage Guarantee
    Math.max(a.atk * 4 - b.def * 2, 1)

  7. Using Variables
    a.atk * 4 - b.def * 2 + v[10]

  8. Conditional (ternary)
    a.hpRate() < 0.3 ? a.atk * 6 : a.atk * 4

  9. Element Rate
    (a.atk * 4 - b.def * 2) * b.elementRate(2)

Practical Full Examples

Balanced Physical Skill
Math.max(a.atk * 4 - b.def * 2, a.atk)

Magic with Level Scaling
a.mat * 3 + a.level * 8 - b.mdf * 1.5

True Damage (ignores defense)
a.atk * 3

Execute (stronger under 25% HP)
b.hpRate() < 0.25 ? a.atk * 8 : a.atk * 3

Important Notes & Common Pitfalls

  • Variance is applied after the formula.
  • Critical hits multiply the final result (default ×3) after formula + variance.
  • Guard halves damage after everything else.
  • Division by zero will crash the game. Always protect it:
    a.atk / Math.max(b.def, 1)
  • Very large numbers can cause issues. Prefer keeping values reasonable or using Math.floor().

Quick Reference Cheat Sheet

a.atk * 4 - b.def * 2 // Basic physical
a.mat * 4 - b.mdf * 2 // Basic magical
Math.max(a.atk * 4 - b.def * 2, 1) // Minimum 1 damage
b.mhp * 0.2 // 20% max HP
a.level * 10 + a.atk * 2 // Level scaling
a.hpRate() < 0.5 ? a.atk * 5 : a.atk * 3 // Conditional

Feel free to ask questions or share your own formulas below.
Happy formula crafting!

2 Likes