A common misconception in League of Legends is that Armor and Magic Resistance lose value above 100 or 200 points because the percentage on your tooltip rises more slowly. In reality, resistance scaling is strictly linear: each point of Armor or MR requires enemies to deal an extra 1% of your Health in raw physical or magic damage to kill you.
Going from 0 to 100 Armor moves you from 0% to 50% damage reduction (doubling your physical Effective HP), and going from 100 to 200 Armor moves you from 50% to 66.7% reduction (tripling your base Effective HP). Both steps add the exact same amount of survivability. The real itemization question is whether your next gold is better spent widening your Health pool or multiplying it with Armor and MR.
How Armor, MR, Heals, and Shields Multiply Into Effective HP
When incoming resistance R (Armor for physical damage, MR for magic damage) is zero or positive, League of Legends calculates post-mitigation damage with the multiplier 100 / (100 + R). Flipping that fraction gives your Effective HP (EHP), which is the raw pre-mitigation damage you can absorb before dying:
Effective HP = (Base HP + Bonus HP + Heals + Lifesteal + Omnivamp + Shields) × (1 + R / 100).
Notice what sits inside the first parenthesis: every point of healing, regeneration, lifesteal, omnivamp, and shielding you receive during combat is multiplied by your Armor and MR just like your starting Health bar. A fighter with 2,500 HP who heals 500 HP from Sundered Sky and lifesteal and triggers a 400 HP Sterak’s Gage shield has a 3,400 raw combat pool. At 150 Armor (a 2.5× multiplier), that fighter absorbs 8,500 physical damage, which is 2,250 more Effective HP than their static 2,500 HP bar suggests.
Baseline Table: Optimal Armor and MR by Health Pool
Before adding sustain or enemy penetration, we can find the exact gold-efficiency equilibrium from basic component prices. A Ruby Crystal grants 150 HP for 400 gold (2.67 gold per 1 HP), while a Cloth Armor (15 Armor for 300 gold) and a Null-Magic Mantle (20 MR for 400 gold) both cost 20 gold per 1 point of resistance. Against a single damage type, marginal Effective HP per gold is equal when HP = 7.5 × (100 + R), or R = (HP / 7.5) − 100. Against a 50/50 split of physical and magic damage where you must buy both Armor and MR (40 gold to raise both by 1 point), the equilibrium shifts to R = (HP / 15) − 100.
Optimal Armor & MR by Max Health (Baseline Without Sustain, Shields, or Penetration)
Single-threat column maximizes EHP per gold against 100% physical or magic damage (R = HP / 7.5 − 100). Balanced column maximizes EHP per gold against a 50/50 physical/magic split (R = HP / 15 − 100).
| Max Health (HP) | Single-Threat Armor or MR | Balanced Armor + MR (Each) | Single-Threat Effective HP |
|---|---|---|---|
| 1,500 HP | 100 | Base (~50–60, buy HP first) | 3,000 EHP |
| 2,000 HP | 165 | Base (~60–70, buy HP first) | 5,300 EHP |
| 2,500 HP | 235 | 65 | 8,375 EHP |
| 3,000 HP | 300 | 100 | 12,000 EHP |
| 3,500 HP | 365 | 135 | 16,275 EHP |
| 4,000 HP | 435 | 165 | 21,400 EHP |
| 4,500 HP | 500 | 200 | 27,000 EHP |
How to adapt this table in a live game: treat the numbers above as a static-HP baseline. If your kit, runes, or support add 600 to 1,000+ HP in combat healing, lifesteal, or shields (such as Aatrox, Dr. Mundo, Zac, or a carry backed by Lulu or Soraka), count that sustain as extra Health and shift one to two rows higher on the resistance columns, aiming for 30 to 60 more Armor and MR than your displayed max HP bar indicates.
Why Real Fights Are More Complex: Damage Types, Anti-Heal, and Penetration
Mixed damage and true damage: Few enemy compositions deal 100% physical or 100% magic damage, and champion labels can mislead. Kog’Maw, Varus, and Corki deal significant magic or mixed damage from physical-looking builds, while Yone blends physical, magic, and true damage. Flat true damage (Ignite, Darius’s Noxian Guillotine, Camille’s Precision Protocol, Cho’Gath’s Feast) bypasses Armor and MR completely, making raw Health and shields your only buffer. Percent max-HP physical or magic damage (Blade of the Ruined King, Liandry’s Torment) punishes raw Health stacking and demands resistances, whereas percent max-HP true damage (Vayne’s Silver Bolts, Fiora’s Grand Challenge) ignores both Health and resistances, forcing you to buy shields, attack-speed slows like Frozen Heart, or crowd control.
Healing and shield reduction: When enemies build Grievous Wounds (Executioner’s Calling, Oblivion Orb, Bramble Vest, or Mortal Reminder), your healing and lifesteal drop by 40%. When an assassin or marksman builds Serpent’s Fang, incoming shields are reduced by 50% (35% for ranged attackers). Anti-heal and anti-shield shrink the bonus pool inside the Effective HP formula back toward your static max HP, lowering the extra premium on pure resistance stacking.
Enemy penetration and resistance shred: Once an enemy carry completes percentage penetration (Lord Dominik’s Regards, Mortal Reminder, Void Staff, Cryptbloom) or percentage shred (Black Cleaver, Bloodletter’s Curse), 30% to 40% of your total Armor or MR is ignored. At that point, stacking a fourth pure resistance item loses gold efficiency compared to buying Health, shields, or damage-reducing item passives such as Randuin’s Omen (-30% critical strike damage) and Force of Nature. Conversely, when facing flat penetration (Lethality or Sorcerer’s Shoes), buying a single Cloth Armor or Null-Magic Mantle on a low-resistance carry provides the highest survival return per gold in the game.
What Junglers Should Keep in Mind: Monster and Objective Damage Types
Jungle companions heal you as you clear, but early defensive stat shards, sub-components, and objective solos depend on knowing what damage each monster deals. Nearly every camp on Summoner’s Rift deals physical damage, with one camp exception and mixed damage on late-game epic bosses:
- Blue Sentinel, Red Brambleback, Krugs, Crimson Raptors, Murk Wolves, and Rift Scuttler: 100% physical damage on all basic attacks (Raptors deal rapid multi-unit physical hits, making early Armor noticeably healthier on your clear).
- Gromp: The only standard jungle camp whose basic attacks deal magic damage, scaling with monster level.
- Elemental Drakes (Infernal, Mountain, Ocean, Cloud, Hextech, Chemtech) and Elder Dragon: Deal physical damage with their primary attacks alongside elemental splash effects (Elder Dragon adds a low-health true-damage execute).
- Voidgrubs, Voidmites, and Rift Herald: Deal physical damage with basic attacks and charges (the Touch of the Void reward buff grants structure-burn true damage to your team, not true damage from the monsters to you).
- Baron Nashor and Atakhan: Deal mixed physical and magic damage. Baron’s primary melee and ranged attacks deal physical damage, while his acid pool, tentacle knockups, and rear spikes deal magic damage, and his Voracious Corrosion aura shreds up to 50 Armor and 25 MR on the player tanking him.
Tower Diving: Turret Damage Type and Built-In Armor Penetration
All lane turrets deal 100% physical damage; Magic Resistance does nothing against tower shots. However, turrets carry two anti-tank mechanics you must calculate before diving: consecutive turret shots on champions ramp up by +40% damage per hit up to a +120% cap (220% total damage from the fourth shot onward), and turrets possess 30% built-in Armor Penetration.
Because of that 30% built-in penetration, a diver with 150 Armor tanks turret shots as if they only had 105 Armor (51% damage reduction instead of 60%). Also note that Plated Steelcaps’ passive attack reduction applies only to basic attacks and does not reduce turret shot damage, though its 25 Armor still counts. Clean dives rely on combining Armor with raw Health or shields and resetting turret aggro before the third and fourth amplified shots land.