How this Pokémon damage calculator works
First, honesty: if you're prepping for a tournament, use a full-Pokédex calculator like Pokémon Showdown's, which knows every base stat, item, and ability in existence. This page is for something different — learning how the damage formula actually works, and running quick manual checks when you already know the numbers. You enter the attacker's level, the move's base power, and the two stats that matter (the attacker's effective Attack or Sp. Atk, and the defender's effective Defense or Sp. Def — after any boosts, drops, or item multipliers). The calculator then runs the genuine Gen V+ formula, floors and all, across all 16 possible damage rolls.
The formula
Level is the attacker's level, Power the move's base power, A the attacking stat, D the defending stat. Every floor() discards decimals — the games do all of this in integer math, which is why hand-calculating with a normal calculator often lands one point high. The random roll takes exactly 16 values (85%, 86%, …, 100%), and damage never drops below 1. One footnote for purists: cartridges apply weather before the random roll; we fold it into the final modifier, which can differ from cart-exact results by a single point in rare cases.
Worked example
A level 50 attacker with 120 Attack uses an 80-power STAB move against a 100 Defense, 130 HP defender that takes ×2 damage:
Step 1: floor(2 × 50 ÷ 5 + 2) = 22
Step 2: floor(22 × 80 × 120 ÷ 100) = floor(2,112) = 2,112
Step 3: floor(2,112 ÷ 50) + 2 = 42 + 2 = 44 base damage
Worst roll: floor(44 × 0.85) = 37 → STAB floor(37 × 1.5) = 55 → ×2 = 110. Best roll: 44 → 66 → 132.
Result: 110–132 damage (average 120.25) — 84.6–101.5% of 130 HP. Only the top roll KOs: 1 in 16, a 6.25% chance. Pray accordingly.
Why damage is a range (and why the floors matter)
Two things make Pokémon damage feel mysterious. The first is the random roll: every damaging move quietly picks one of 16 multipliers between 85% and 100%, which is why your "guaranteed" KO sometimes leaves a smug opponent standing on 3 HP. The range isn't lag or a bug — it's a uniform 16-sided die baked into the engine since 1996. The second is truncation: because the game floors after nearly every step, damage moves in discrete jumps, and two rolls one percent apart often produce the same final number. Look at the 16 rolls behind our example — they produce only nine distinct results. This is also why "does it KO?" is properly answered as a fraction: count the rolls that meet the defender's HP and divide by 16, exactly what the table below the calculator does.
What this calculator deliberately leaves out
Critical hits (×1.5 in Gen VI+), held items like Life Orb (×1.3) and Choice Band (×1.5 to the stat), abilities, EVs, IVs, and natures are all real and all omitted — on purpose. Items, natures, and EVs change your stats, so the fix is simple: enter the final effective stat after those multipliers (a Choice Band Pokémon with 300 Attack? Type 450). Crits and Life Orb are flat multipliers you can approximate with the weather slot in a pinch. What you get in exchange for entering numbers yourself is the thing the big calculators hide: you can watch exactly where each point of damage comes from — which is how you go from memorizing matchups to actually understanding them.