Magic Resistance

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Magic Resistance is an attribute of heroes that reduces Magical damage by a percentage. Heroes can increase their magic resistance with Strength, items, and spells. All heroes innately possess 25% base magic resistance. Some summons also possess magic resistance.

Formula[edit]

Magical damage taken is calculated using the following formula:

actual damage = magical damage × (1 - strength resistance) × (1 - innate resistance) × (1 - first resistance bonus) × (1 - second resistance bonus) × (1 + first resistance malus) × (1 + second resistance malus)

Magic resistance is calculated as follows:

total magic resistance = 1 - ((1 - strength resistance) × (1 - innate resistance) × (1 - first resistance bonus) × (1 - second resistance bonus) × (1 + first resistance malus) × (1 + second resistance malus))

Example: Anti-Mage on level 7 with maxed Counterspell and a Hood of Defiance has a magic resistance of:
1 - ((1 - (23 + 1.3 x 6) × 0.0008) × (1 - 0.25) × (1 - 0.45) × (1 - 0.25))
1 - (0.97536 x 0.75 x 0.55 x 0.75) = 69.8248%

As seen in the formula above, magic resistance is calculated multiplicatively. Magic resistance items may also stack with each other the same way. Because of the way it is calculated, it is impossible to reach 100% magic resistance without it being specifically given by an ability. It also means that 100% magic resistance buffs cannot be reduced.
Magical damage can also be amplified, and is also multiplicative.

Example: Crystal Maiden on level 12 is ethereal and under the effect of Veil of Discord's Magic Weakness:
1 - ((1 - (18 + 2 x 11) × 0.0008) × (1 - 0.25) × (1 + 0.4) × (1 + 0.18)
1 - (0.968 × 0.75 × 1.4 × 1.18) = -19.9352%