Spell damage ( ${\displaystyle Sp}$ ) is usually damage dealt in a separate instance from attack damage, with some exceptions. This includes all abilities (including item abilities and attack modifiers) which deal the 2 damage types — physical or pure damage.

Physical spell damage is influenced by armor and pure damage is not affected by either. All three underlie damage manipulation.

Spell Damage Manipulation

Stacking

All sources of spell damage manipulation stack additively within two categories, outgoing and incoming, which are then multiplied together. The two categories Outgoing Spell Damage Manipulation and Incoming Spell Damage Manipulation stack additively with Generic Incoming Damage Manipulation and Generic Outgoing Damage Manipulation respectively as spell damage manipulation is considered to be just a part of Damage manipulation. Since these are handled separately, the same category stack additively while different categories stack multiplicatively with each other.

For example, spell damage dealt by summons, unless otherwise stated, are not affected by the outgoing spell damage manipulation of the hero. However, summons can be affected by incoming spell damage manipulation since incoming spell damage manipulation affects the target of the damage instead of the caster.

Spell Damage Multiplier is defined as:

${\displaystyle \text{Spell Damage Multiplier} = \big( 1 + \sum (\text{Outgoing Manip}) \big) \times \big( 1 + \sum (\text{Incoming Manip}) \big) }$

Example 1: Outgoing Manipulation

Bloodseeker with a level 4 Bloodrage buff with Kaya and Sange. What is his current spell damage multiplier?

Spell damage amplification values:

• Level 4 Bloodrage: 0.3
• Kaya and Sange: 0.12

${\displaystyle Sp_{Mu} = (1 + 0.3 + 0.12) \times (1 + 0) = 1.42 }$

Bloodseeker's spell damage multiplier is 1.42 in this example.

Example 2: Incoming and Outgoing Manipulation

Bloodseeker from the previous example has Dagon 5 and is affected by Mage Slayer. How much actual spell damage Energy Burst will be dealt to Marci

• Dagon 5 spell damage: 800

Marci affected by spell damage from Bloodseeker in this example.

Example 3: Generic Damage Manipulation

Bloodseeker from the previous example instead chooses to cast his Dagon 5 on a Spectre with level 4 Dispersion.

Dispersion is generic damage manipulation, meaning it affects all damage dealt to Spectre. Despite this, it stacks additively with other incoming spell damage manipulation

• Dagon 5 spell damage: 800
• Incoming Generic Damage Manipulation: Dispersion: -0.2
• Outgoing Spell Damage Manipulation: Bloodrage: 0.3, Kaya and Sange: 0.12, Mage Slayer: -0.25

${\displaystyle {\begin{aligned}Sp_{Mu}&=\underbrace {(1+(0.3+0.12-0.25))} _{\text{Outgoing}}\times \underbrace {(1+-0.2)} _{\text{Incoming}}\\&=\underbrace {(1.17)} _{\text{Outgoing}}\times \underbrace {(0.8)} _{\text{Incoming}}\\&=0.936\end{aligned}}}$

${\displaystyle {\text{Total Spell Damage}}=800*0.936=748.8}$

Spectre affected by will take 748.8 spell damage from Bloodseeker in this example.

Outgoing Spell Damage Manipulation

A unit that has outgoing spell damage manipulation deals more or less spell damage with any spell damage they apply to any unit. Multiple sources of outgoing spell damage manipulation stack additively.

¹ Requires talent.

^2a Requires Aghanim's Scepter.

^2b Requires Aghanim's Shard.

Talents

Spell Damage Amplification

Ability
Passive

Affects
Self

Damage
Physical

There is no description for this ability.

Spell Damage Amp: Varies

• Increases the hero's outgoing spell damage amplification.

• The following values exist:
  • 3%/4%/5%/6%/7%/8%/9%/10%/11%/12%/14%/15%/16%/18%/19%/20%/25%

The following heroes have a talent that grants them outgoing spell damage amplification.

Item Sources

Many items grant their owners a spell damage amplification bonus by giving them a direct bonus. The effects are limited to the item's owner, which must have the item equipped.

Bonus Spell Damage

Item	Value	Item Cost	Cost/Value Point
Kaya	10	2100	210
Kaya and Sange	12	4050	337.5
Meteor Hammer	10	2850	285
Timeless Relic	15	N/A	N/A
Vambrace (Intelligence)	6	N/A	N/A
Yasha and Kaya	12	4000	333.33
Values do not include portions from actives or auras.

For Kaya-based items: Multiple sources of spell damage amplification do not stack.

Incoming Spell Damage Amplification

A unit that has incoming spell damage amplification debuff on them takes more spell damage, and multiple sources of incoming spell damage amplification stack additively. Incoming spell damage amplification affects every source of spell damage, except for damage flagged as HP Removal.

Abilities

¹ Requires talent.

^2a Requires Aghanim's Scepter.

^2b Requires Aghanim's Shard.

Exceptions

There are certain cases of abilities that ignore both types of spell damage amplification, and those abilities usually cannot spell lifesteal. In general, abilities with health manipulation mechanics (Instant Kill, HP Removal, Delayed Damage etc.) are not affect by both types of spell damage amplifications.

However, the following abilities are affected by Hunter's Boomerang's incoming spell damage amplification:

¹ The damage of the bouncing attacks are unaffected by outgoing spell damage amplification. The -based damage is fully affected, including that of the bounces.

² The damage of the bouncing attacks are unaffected by outgoing spell damage amplification. However, Overload's area damage is fully affected, including that of the bounces.

³ The damage of the bouncing attacks count as spell damage, but are unaffected by outgoing spell damage amplification.

Version History

Patch History