Armor Damage Mitigation Calculator
Armor in most modern games reduces incoming damage by a fraction calculated as armor divided by (armor plus a constant k). This diminishing-returns formula ensures that armor never reaches 100% mitigation and that each additional armor point provides less benefit than the last. This calculator shows damage reduction percentage, effective HP multiplier, and actual damage taken from a given incoming hit, helping players and designers understand armor scaling across the full range of values.
Armor mitigation formula
Damage reduction = armor / (armor + k)
Damage taken = raw damage * (1 - reduction)
Effective HP = base HP / (1 - reduction)
At armor = k, the reduction is 50%. At armor = 0, reduction is 0% (no mitigation). As armor approaches infinity, reduction approaches but never reaches 100%.
Armor scaling in game design
- Setting k equal to the average armor of a fully geared character means that character reaches 50% physical damage reduction at endgame, a common balance target.
- At armor = k/3, damage reduction is 25%; at armor = 3k, it is 75%. This gives designers a predictable scaling curve.
- Armor penetration mechanics in games work by reducing the effective armor value in this formula, shifting the mitigation curve downward for the attacker.
- Effective HP scales hyperbolically with armor, not linearly. Going from 0 to k armor doubles effective HP; going from k to infinity armor also effectively doubles it toward 4x.
Armor damage mitigation: frequently asked questions
What is the armor mitigation formula?
The standard game design formula is damage reduction = armor / (armor + k), where k is a game-specific constant. This gives diminishing returns: the more armor you have, the less each additional point reduces damage. Damage taken = raw damage * (1 - reduction).
Why do games use diminishing returns on armor?
Diminishing returns prevent armor from ever reaching 100% damage reduction (infinite effective HP) and keep the game balanced. Without it, a sufficiently high armor value would make a character completely invulnerable, which breaks combat design.
What is the k constant and how is it set?
The k constant determines the armor value at which you reach 50% damage reduction (armor = k gives 50%). Designers set it based on typical armor ranges in the game. Common values are 100, 1000, or the intended baseline armor for a fully geared character.
What is effective HP?
Effective HP is the total raw damage a character can absorb before dying, accounting for mitigation. Effective HP = base HP / (1 - damage reduction). A character with 1,000 HP and 50% reduction has 2,000 effective HP.
Is there a linear armor formula instead of diminishing returns?
Some games use linear percent reduction capped at a maximum (e.g., 75%). This calculator uses the diminishing-returns formula, which is more common in games like League of Legends, Diablo, and Path of Exile.
Official sources
- NIST/SEMATECH e-Handbook of Statistical Methods: itl.nist.gov/div898/handbook/.
- National Council of Teachers of Mathematics: nctm.org.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.