Working out how much damage you actually deal to a resistant or immune monster in Diablo 2: Resurrected is one of the most confusing parts of build planning. Resistances stack in non-obvious ways, immunity breaking only works at a fraction of its listed value, and sunder charms changed the rules again. We built a free Resistance & Damage Calculator that does the math for you — and models the real mechanics rather than a simplified guess.

You pick a damage type, enter the monster's resistance and your skill damage, then layer in every reduction you actually have — a sunder charm, Conviction, Lower Resist, Amplify Damage or Decrepify, Cold Mastery, and any -% enemy resistance from gear or facets. The tool tells you whether the immunity breaks, the effective resistance, and your real damage output, with a plain-English breakdown of how each source was applied.

Why It's Not As Simple As Subtracting

In D2R a monster with more than 99% resistance is immune and takes no damage until its resistance is dropped below 100%. Only four effects can break an immunity — Conviction and Lower Resist for elemental, Amplify Damage and Decrepify for physical — and against an immune monster they work at just 1/5 of their listed value. That 1/5 penalty is the part most people get wrong, and it's exactly what the calculator handles automatically.

Sunder charms add another layer: holding one sets an immune monster's resistance to 95%, after which Conviction, Lower Resist and Cold Mastery apply at 1/5 while -% enemy resistance from gear stays at full. And gear-based -enemy resistance does nothing at all while a monster is still immune — it only kicks in once the immunity is broken. The tool tracks all of these interactions so you can see, for example, whether your Conviction is strong enough to crack a specific immunity on its own.

Real Monster Data, Not Guesses

The calculator includes target presets pulled straight from the game's monster data and cross-checked against published references. That includes the Hell act bosses (Andariel actually has -50% fire resistance, so she takes extra fire damage), the Travincal Council's fire-immune and lightning-immune types, and the Uber Tristram and Pandemonium bosses with their exact immune values — Uber Mephisto is both lightning and poison immune, Uber Diablo is fire immune, Uber Baal is cold immune.

You can also model champion and unique packs. Boss-pack enchantments add resistance to a single element — Stone Skin grants +100% physical in Hell, while Fire, Cold, and Lightning Enchanted each add +75% — which is how a pack can become immune to an element the base monster isn't. Select an enchantment and the calculator factors it in.

Where To Find It

The Resistance & Damage Calculator is live now and free to use, with no account needed. It sits alongside our other D2R planning tools, including the Hell Immunity Calculator for picking safe farming areas and the IAS Calculator for attack-speed breakpoints. If you're theorycrafting a build that has to punch through immunities, it should save you a lot of spreadsheet math.