Here’s How Armor Works in Dota Underlords

How does Armor work in Dota Underlords

How much damage does a Chainmail’s +10 Armor reduce?

And how much bonus damage do you get from Blight Stone’s -3 Armor?

This quick guide will explain in detail how Armor works in Underlords.

Spoiler alert—lots of maths and economics in this article for all you nerds!

How does Armor work in Dota Underlords?

In Dota Underlords, items, abilities, and Alliance effects may increase or reduce a unit’s Armor.

Armor is a stat that reduces incoming physical damage by a percentage.

Conversely, when a unit’s Armor is reduced, it takes more damage.

For each point of Armor a unit has, its HP essentially increases by 5.8%. This is called the Effective HP.

Effective HP (EHP) is the unit’s base HP, plus the extra damage he can take due to the Armor’s damage reduction.

Here are some examples for a unit with 1,000 HP:

  • 1 Armor = 1,058 EHP
  • 2 Armor = 1,116 EHP
  • 5 Armor = 1,290 EHP
  • etc…

It gets a little complicated though. The increased EHP scales up for each point of Armor. At 30 Armor and above, the EHP increase per Armor is at 7.7%.

Armor doesn’t work on Magical & Pure Damage

Armor calculation only takes effect on Physical Damage, both from normal attacks or hero spells (some spells deal Physical Damage).

Magical Damage and Pure Damage will ignore Armor, whether it’s an increase or a reduction.

For example, Mage skills like Lina’s Laguna Blade or the Demon’s Pure Damage effects will ignore increased or reduced Armor.

A better way to calculate Armor

Here’s an easier way to estimate Armor bonuses.

At 0–15 Armor, you can approximate that each point gives around ~6% EHP:

  • 1 Armor = +6% More HP
  • 5 Armor = +30% More HP
  • 10 Armor = +60% More HP
  • 15 Armor = +90% More HP

At 15–30 Armor it might start to get a little complicated. At this range the EHP bonus scales up to ~7% and above.

  • 20 Armor = +120% More HP
  • 30 Armor = +200% More HP

Don’t forget to include the unit’s Base Armor! A unit with 5 Base Armor for example will have a total of 15 Armor when equipped with a Chainmail (+10 Armor).

Also note that a unit’s Armor can go negative.

Armor Damage Multiplier Table

The way Armor is actually calculated in the game is through damage multipliers. These are multiplied to the incoming damage taken. Here is the formula:

Damage multiplier = 1 – ((0.052 × armor) ÷ (0.9 + 0.048 × |armor|))

So much maths! Here’s a human readable chart to see the damage multipliers per point of Armor. (Source)

Armor (+)MultiplierArmor (-)Multiplier

Another Example — Chainmail vs. Vitality Booster

Here’s another example. Let’s say you have a unit with 500 HP and 0 Base Armor.

You’re offered a Vitality Booster (+250 HP) and a Chainmail (+10 Armor), which one do you choose?

Chainmail item in Dota Underlords

The Chainmail gives the unit an additional 10 Armor, which as we now know is 60% more HP.

Therefore Chainmail gives 500 * 0.60 = +300 HP which is a bit higher than the Vitality Booster’s bonus HP.

Plus, this bonus scales well too as the unit levels up and gains more HP.

This is why Armor effects are almost always better than increased HP bonuses.

Which units should you give Armor?

Armor is more effective on units with lots of HP.

Why? Well as you learned, Armor increases a unit’s effective HP by a certain percentage.

Since Armor is a multiplier, it is only as good as the amount of HP a unit has.

20 Armor is useless on a unit with 200 HP but much more effective on 1,000 HP.

In addition, units with more HP can survive longer on the board, so you’ll get more value out of items like Chainmail as it reduces more damage throughout the duration of the round.

How much Armor is enough?

Armor has diminishing returns. Check out this graph that shows the relationship between armor (X-axis) and damage multiplier (red line). (Source)

Armor effective HP damage multiplier graph

As you can see, the damage multiplier slows down in a curve at around 20-30 Armor. This means that the more Armor a unit already has, the lesser the damage is reduced for every succeeding point.

The difference between 0 to 5 Armor has much more impact than the difference of say 20 to 25 Armor. (You can also see this pattern in the Damage Multiplier table above.)

In general, try not to get a unit’s Armor to 30 and above.

So in summary:

  1. Armor is better on units with lots of HP
  2. Armor is better on units with less Armor

Which units should have Armor reducing effects?

For damage reduction items such as Blight Stone, equip them to your DPS units that you think will survive the longest or can deal the most amount of damage such as Assassins and Hunters.

Blight Stone item in Dota Underlords

Armor can go negative if the target has 0 Base Armor. This helps for easy pick-offs as Assassins backstab the squishy Mages and Supports in the backlines.

The Heartless synergy effect is also very effective on a physical damage lineup such as Hunters.

How much Armor reduction is enough?

Negative Armor reduction also has diminishing returns.

The more negative a unit’s Armor is, the lesser the effect of every succeeding reduction.

Again, using the line chart and the damage multiplier table above, you can see that around -15 to -20 Armor, there’s not much significant effect.

How to Increase/Reduce Armor

Now that you know how armor works, here’s how to increase or reduce Armor.

Alliance effects

  • 3/6/9 Warriors will give them 10/15/25 bonus Armor
  • 2/4/6 Heartless will reduce enemy Armor by 5/10/20
  • 3/6 Scrappy will give a random/all allies +9 Armor and 8 HP Regen. Armor and HP are doubled if you start the fight with fewer units than your opponent.


  • Blight Stone — Target gets -3 Armor
  • Chainmail — +10 Armor
  • Assault Cuirass — Equipped hero and adjacent allies have +15 Attack Speed and +10 Armour. Adjacent enemies have -15 Attack Speed and -10 Armour
  • Shiva’s Guard — +10 Armour. Emits a freezing wave that deals 250 damage to enemies within 3 cells and slows their movement and attack speed for 4s. (once per battle)

Hero Abilities

  • Alchemist’s Acid Spray AoE skill reduces enemy Armor by -5/-8/-11
  • Axe’s Berserker Call gives him 15/25/35 bonus Armor
  • Slardar’s Corrosive Haze reduces a single target’s Armor by -15,-30,-45 for 20 seconds


Hopefully this article gives you a good grasp on how Armor works and will help you make better decisions in Dota Underlords.

Got any more tips and questions? Drop a comment down below.

3 thoughts on “Here’s How Armor Works in Dota Underlords

  1. This article begins by saying armor stacks get better the more you have, then it says that the armor has diminishing returns. At what point does armor become less viable? What are the percentages?

  2. The idea of diminishing return is flawed as seen in the calculation of EHP. EHP actually gets better as armor goes up.

    The reason is – even though the effectiveness of damage reduction goes down as armor goes up, the unit has more HP left after each attack which can be used to take more damage. This explains why EHP scales linearly at 6% and even better at 7% after 30 armors.

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