How damage is calculated in LoL: mitigation, penetration and EHP
The number you see floating over a champion is almost never the ability’s “raw” damage: it’s what’s left after mitigation. Understanding the resistance formula, the penetration order and effective HP lets you predict combos and build with intent.
From raw damage to real damage: the resistance formula
Armor mitigates physical damage and magic resist mitigates magic damage, both with the same formula. For a resistance R ≥ 0, incoming damage is multiplied by 100 / (100 + R). With 100 armor you take half the physical damage (100 / 200 = 0.5); with 200, a third (100 / 300 ≈ 0.33).
Notice something important: the formula never reaches 0. Each point of resistance adds a bit of mitigation, but with diminishing returns as a percentage. In effective HP, however, the return is linear, as you’ll see below.
When a resistance is negative (from reductions or penetration that pushes it below 0), the other branch of the formula is used: the multiplier is 2 − 100 / (100 − R). With R = −100, damage is multiplied by 1.5: you take 50% more. Negative resistance amplifies damage instead of reducing it.
True damage ignores this formula entirely: it goes through unmitigated by armor or MR. That’s why it’s so valuable against very tanky targets.
multiplicador = 100 / (100 + R) (R ≥ 0)
multiplicador = 2 − 100 / (100 − R) (R < 0) | Armor | Reduction | Damage from 1000 | EHP with 2000 HP |
|---|---|---|---|
| 0 | 0% | 1000 | 2000 |
| 25 | 20% | 800 | 2500 |
| 50 | 33.3% | 667 | 3000 |
| 100 | 50% | 500 | 4000 |
| 150 | 60% | 400 | 5000 |
| 200 | 66.7% | 333 | 6000 |
| 300 | 75% | 250 | 8000 |
The mitigation engine with the real formula: damage taken = damage × 100 / (100 + armor).
Effective HP (EHP): why resistance and health multiply
Effective HP measures how much raw damage of one type you survive before dying. Against a single damage type, EHP = HP × (1 + R/100). With 2000 health and 100 armor, your physical EHP is 2000 × 2 = 4000: it takes 4000 raw physical damage to kill you.
Here’s the part that surprises many people: in EHP, every point of resistance is worth the same. Going from 0 to 100 armor doubles your physical EHP; going from 100 to 200 raises it again by the same absolute amount of health (another 100% of your base HP). Resistance has no “diminishing returns” for survivability — that intuition comes from looking at the mitigation percentage, not effective HP.
That’s why health and resistance amplify each other. Buying armor is more valuable the more health you have, and vice versa. We cover it in health vs resistances. A tank balances both: pure health melts to percent penetration and magic damage; pure resistance gets shredded by true damage and max-health percentages.
In the site’s mitigation tool you can input HP, armor and MR and see EHP against physical, magic and mixed damage, plus the “sweet spot” where buying more health or more resistance pays off.
| Health \ Armor | 0 | 25 | 50 | 100 | 150 | 200 | 300 |
|---|---|---|---|---|---|---|---|
| 1200 | 1200 | 1500 | 1800 | 2400 | 3000 | 3600 | 4800 |
| 1800 | 1800 | 2250 | 2700 | 3600 | 4500 | 5400 | 7200 |
| 2400 | 2400 | 3000 | 3600 | 4800 | 6000 | 7200 | 9600 |
| 3000 | 3000 | 3750 | 4500 | 6000 | 7500 | 9000 | 12000 |
Effective HP against physical damage, computed by the engine for each combo. Health and armor multiply each other: that’s why the highest EHP (deep green) is when you raise both together, not just one.
Penetration and lethality: the order matters
Penetration reduces the target’s resistance before the formula is applied. It always applies in this order: first percent reduction (effects that lower armor, like certain runes or abilities), then percent penetration (a % of the remaining resistance you ignore), and finally flat penetration / lethality.
The order isn’t a detail: since each step operates on what the previous one left, applying them in reverse would give a different number. The mental rule is “multiplicative first, flat last”.
Lethality is flat armor penetration. In older patches it scaled with level; for this guide, treat it as direct flat pen: it subtracts that many points of effective armor from the target. Flat magic penetration works the same way against MR. We break it down in penetration and lethality.
Crucial rule: penetration never takes effective resistance below 0. If the target has 20 armor and your lethality is 30, their effective armor lands at 0, not −10. Only reductions (a different effect from penetration) can push a resistance into negative territory and trigger the amplification formula.
| Effective armor | Damage taken (of 1000) | |
|---|---|---|
| No penetration | 100 | 500 |
| Last Whisper (18% pen) | 82 | 549 |
| Black Cleaver (30% red.) | 70 | 588 |
| Serrated Dirk (10 pen pl.) | 90 | 526 |
Computed with the engine (effectiveResist) on a target with 100 armor. Lethality scales with level.
An ability’s damage, step by step
An ability’s raw damage is base + Σ(coefficient × stat), computed per rank. An ability can have several coefficients: for example +0.6 AP and +0.3 bonus AD. Ranking up raises the base (and sometimes the coefficient); raising your stats raises the scaled part.
Example: a rank-3 ability with 200 base and 0.7 AP, with 300 AP, deals 200 + 0.7 × 300 = 410 raw damage. If it’s magic damage and the target has 60 effective MR (after penetration), the multiplier is 100 / 160 = 0.625, so the real damage is 410 × 0.625 ≈ 256.
The full order for one hit is: compute raw damage from rank and stats → determine the target’s effective resistance by applying reduction, % penetration and flat penetration in that order → multiply raw damage by 100 / (100 + R_effective). True damage skips the last step.
For combos, add up the real damage of each hit, not the raw, and remember that items like Guinsoo’s or mid-combo reductions change the effective resistance between hits. The site’s versus and build tools run this math with the exact patch values so you can see whether a combo kills or not.
1000 physical damage into 100 armor and a 300 shield, in the REAL order the game processes it: amplifiers first, then resistance mitigation (×0.5 at 100 armor), then the shield (absorbs 300), and what’s left hits health. The order explains why a well-timed shield or a point of armor is worth so much.
FAQ
Does 100 armor mean I take 100 less damage?
No. Armor doesn’t subtract flat damage: it multiplies it by 100 / (100 + R). With 100 armor you take half the physical damage, whether the hit was 100 or 1000. In effective-HP terms, 100 armor is like doubling your health against physical damage.
What’s the difference between flat and percent penetration?
Percent penetration ignores a % of the target’s remaining resistance and applies before flat; flat penetration (lethality included) subtracts fixed points at the end. That’s why percent shines against high-resistance targets and flat against low-resistance ones. Neither takes effective resistance below 0.
Why is more health sometimes better than resistance, or vice versa?
Because health and resistance multiply in effective HP: you want to buy whichever you’re more “unbalanced” in. If you already have lots of health, adding resistance pays off more, and vice versa. It also depends on the enemy: against true damage or max-health %, resistance loses value; against flat burst, health helps you survive a combo.