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Dota 2 Damage Calculator: Armor and Magic Resist

See how much damage actually lands after armor, magic resistance and spell amp. The formula is checked against Liquipedia, and the two places where the calculator assumes something are flagged.

Damage dealt

100

Damage reduction
0.0 %
  • Valve does not publish these formulas. The 0.06 armor constant and multiplicative resist stacking come from open sources and were cross-checked against each other.

Unofficial tool. Not affiliated with Valve Corporation. Formulas are reconstructed from open sources and may drift from the game after patches.

How we calculate

Physical damage is cut by armor using the Liquipedia formula: reduction = 0.06 × armor / (1 + 0.06 × |armor|). The absolute value in the denominator is not a typo — it is what makes negative armor amplify damage instead of breaking the formula. The 0.06 factor was fetched live on 2026-08-18.

Magic damage first meets the base 25 % resistance, and every resistance source stacks multiplicatively: total = 1 - ∏(1 - resist_i). Spell amp is applied on top of that. ⚠️ Two steps are the calculator decision rather than a quote from the source: capping total resistance at 80 % and adding spell amp sources together. Pure damage is touched by neither armor nor resistance.

Sources

checked 18 August 2026

Questions and answers

Why does armor not just subtract damage?

Armor follows a saturation curve: every additional point adds less than the one before. That is why 30 armor does not make you immune — it removes a fraction of the damage that only approaches a limit asymptotically.

Why does magic resist multiply instead of adding up?

Resist sources stack multiplicatively: two 50% sources give 75%, not 100%. That is exactly why you cannot stack resist forever — each new source only cuts damage that has already been cut.

What does the 80% cap do?

It is our guard rail, not a game rule: the calculator does not take total resist above 80%. None of the sources we checked states such a cap, so wherever it engages we label it explicitly.

How is spell amp calculated?

Multiple spell amp sources add together, and the result multiplies whatever survived the resist step. ⚠️ The additivity of spell amp is not directly confirmed in the sources we checked.

Why does pure damage never change?

Pure damage ignores both armor and magic resist by definition. Only specific effects reduce it, and those are not modelled in this calculator.

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Unofficial tool. Not affiliated with Valve.