League of Legends Damage Calculator

League of Legends uses a two-layer damage system that separates physical damage and magic damage, each mitigated by its own defensive stat. Understanding how these interact with your champion's ratios, penetration items, and the target's resistances is the foundation of effective champion building and team fight calculations.

Every ability or auto attack that deals damage starts with a raw damage value — the number before resistances apply. For physical abilities and auto attacks, raw damage is calculated from base damage plus a fraction of your bonus attack damage (AD). For magic abilities, raw damage comes from ability power (AP) scaled by the ability's AP ratio. Some abilities deal both types simultaneously, which this LoL damage calculator handles by summing both components.

Once raw damage is established, the game applies the target's effective resistances. Armor reduces physical damage and magic resist (MR) reduces magic damage, both using the same mathematical formula: damage taken equals 100 divided by (100 plus the effective resistance). A target with 100 armor takes exactly 50% of incoming physical damage; one with 200 armor takes only 33.3%.

This damage-reduction formula means resistances follow a law of diminishing returns — going from 0 to 100 armor saves the same absolute percentage as going from 100 to 200, but the incremental value of each additional point shrinks as resistances stack higher. Penetration items exploit this by reducing effective resistance before the multiplier is applied, making each penetration point more valuable against heavily armored targets.

The League of Legends damage calculator on this page faithfully implements all of these mechanics: lethality-to-flat-pen conversion, percent armor penetration, and final physical and magic multipliers. Use it to plan item builds, compare champion matchups, and understand how much true damage you are effectively dealing after resistances.

The formulas above directly mirror the JavaScript code powering this calculator. Two subtleties are worth highlighting for players who want to build optimally.

First, lethality scales with champion level. At level 1, one point of lethality converts to only 0.622 flat armor penetration. By level 18, one point converts to exactly 1.0 flat armor penetration. This means lethality items are weaker in the early game and reach their full efficiency only at max level. The formula is: Flat Armor Pen = Lethality × (0.6 + 0.4 × Level / 18).

Second, percent armor penetration is applied before flat penetration. If a target has 200 armor and you have 30% armor pen plus 20 lethality at level 18, the calculation is: 200 × (1 − 0.30) = 140 armor after percent pen, then 140 − 20 = 120 effective armor. Reversing the order would give a meaningfully different result, so the ordering matters for planning your item purchases.

The physical damage multiplier (100 / (100 + effectiveArmor)) is a well-known diminishing-returns curve. At 0 effective armor, you deal 100% of raw physical damage. At 100, you deal 50%. At 300, you deal 25%. Understanding this curve helps you decide when stacking more armor penetration beats simply buying more raw AD.

One of the most common questions among AD-focused players is whether to prioritize percent armor penetration (such as Last Whisper upgrades) or lethality (flat armor penetration from items like Serrated Dirk, Lethality Dirk, and their upgrades). The answer depends entirely on the target's armor value and your champion's level.

Percent armor penetration shines against high-armor targets. If an enemy tank has 300 armor, 30% armor pen removes 90 points — far more than lethality items provide. Against a 50-armor squishy, that same 30% removes only 15 points, making lethality (which gives a flat reduction) more efficient.

Lethality is most valuable against targets with low to moderate armor, typically the squishy carries and mid laners in the enemy team. A full lethality build can effectively reduce a squishy's armor to near zero or even negative effective armor does not apply — effective armor is floored at zero — meaning further flat penetration beyond the target's armor is wasted.

The crossover point where percent penetration becomes more efficient than an equivalent amount of lethality depends on target armor and champion level. As a general rule of thumb: buy lethality to assassinate squishies and buy Last Whisper upgrades when the priority targets have 150+ armor. Mixing both is often optimal in practice, since your team faces both tanks and carries.

This LoL damage calculator lets you test these scenarios directly. Input real armor values from champion builds and compare the resulting physical damage to decide which penetration path maximizes your output against specific matchups.

Magic damage in League of Legends follows an identical mitigation formula to physical damage but uses the target's magic resistance (MR) stat instead of armor. The magic damage multiplier is 100 / (100 + effectiveMR), where effective MR in this calculator equals the target's base MR floored at zero (MR penetration items are not included as a separate input since they are separate from the AP scaling inputs).

AP champions care deeply about the enemy's MR because it scales linearly with damage loss. A mid-lane mage dealing 500 raw magic damage against a target with 100 MR will land only 250 damage — a 50% loss. The same mage against a target with 50 MR will land 333 damage. Itemizing around this gap is the core skill expression for AP players.

When evaluating your AP build, enter the target's expected MR in the calculator along with your AP total and the ability's AP ratio. The output shows you the exact post-MR damage, letting you decide whether building more AP or switching to a void staff (which provides percent MR penetration) will scale better into the match.

Some abilities deal mixed damage, scaling off both AD and AP ratios. The calculator handles these by computing physical and magic components separately and adding them. For example, an ability with 100 base damage, 60% bonus AD scaling, and 30% AP scaling with 200 bonus AD and 150 AP would yield: Physical Raw = 100 + (200 × 0.60) = 220; Magic Raw = 150 × 0.30 = 45. Each component is then reduced by its corresponding resistance before the totals are summed.

The most powerful use of a League of Legends damage calculator is comparing item paths before you spend gold. Instead of guessing which item gives more damage, you can enter the stats each item provides and immediately see the real output difference against a specific target build.

To simulate an item comparison, start with your current in-game stats as the baseline. Then increase the relevant stat (bonus AD, AP, lethality, or armor pen percent) by the amount the new item adds, and read off the new total damage output. Repeat for the alternative item. The calculator's instant feedback removes the guesswork from mid-game build decisions.

Build planning also helps you recognize diminishing returns on raw stats. If you already have 400 bonus AD and 0 armor penetration against a target with 150 armor, adding another AD item may increase your physical raw damage by 50 points but the resistance multiplier cuts that gain significantly. A penetration item that lowers effective armor from 150 to 100 raises your multiplier from 40% to 50% — a 25% relative increase applied to all your existing physical damage, which can far outstrip the flat damage gain from more AD.

Use the champion level field to simulate different game stages. At level 9, your lethality converts at roughly 0.80× efficiency; at level 18 it is at full 1.0×. Planning a mid-game power spike versus a late-game scaling champion? Enter the expected level for each window to see which champion wins the damage race at that point.

Pro tip: combine the calculator with publicly available champion stat databases. Look up a target champion's expected armor and MR at the level you intend to fight them, enter those values, and you get a reliable estimate of how much damage you will deal in a real game scenario rather than relying on vague intuition.

Beyond physical and magic damage, League of Legends has a third damage type — true damage — that bypasses all resistances and is not calculated by this tool because it requires no mitigation math. True damage is the rarest type and appears on specific abilities and items. Knowing when an ability deals true damage versus physical or magic damage is important for understanding why some champions ignore tank builds.

This calculator covers the two mitigation-dependent damage types in depth. Physical damage includes all basic attacks, most AD-scaling abilities, and on-hit effects that specify physical damage. Magic damage includes most AP-scaling abilities, certain on-hit effects (like Wit's End's magic damage), and abilities explicitly tagged as magic.

Mixed-damage abilities, where a single skill has both a physical component and a magic component, are common. Riot designs these to be partially effective against either armor or MR stacking, requiring enemies to buy both types of resistance to fully counter a champion. This calculator is particularly useful for those abilities since it computes both components simultaneously and shows you the breakdown.

When planning your item build against a specific target, always check the enemy champion's item path. A support building Gargoyle Stoneplate and Thornmail is dramatically different from one buying Moonstone and Redemption. The former will have 200+ armor and MR; the latter may stay near base resistances. The same build that destroys one enemy support deals far less to the other.