Lethality vs Armor Penetration, Live and Future Values

A common phrase I am hearing about the new Lethality, which will be replacing flat armor pen next season, is that it is 'weaker early game but stronger late game'. This is not strictly true and I just wanted to toss out some numbers and math so that people get a better idea of how much benefit or detriment they will be seeing with the new system as compared to live.

First the obvious disclaimer: This is all information gained from the PBE and thus any numbers about lethality calculations or the amount of lethality on items is subject to change.

So without further ado, the lethality formula as found on surrender@20:

"The current formula is 0.4X + [((0.6X * Y)/18) = Flat Penetration Amount], where X is Lethality and Y is target champion level."

For a quick example equation that gets to the heart of this, assume we have 10 lethality and are attacking a level 18 opponent:

.4(10) + ((.6(10) x (18))/18) = 4 + ((6 x 18)/18) = 4 + 6 = 10

So 10 Lethality at level 18 equals 10 armor penetration, and of course at all levels earlier than 18 lethality becomes weaker than armor penetration. So we can immediately see that lethality is not necessarily 'stronger late game' but it is certainly weaker early game.

Of course this is why lethality numbers tend toward a little higher than the flat armor penetration used to be, here are all the current items with armor penetration compared to their future lethality:

Serrated Dirk: Currently 10 Armor Penetration -> 15 Lethality - Level 1-18 Range: 6.5 -> 15 - Evens out with current values at level: 8

Youmuu's Ghostblade: Currently 20 Armor Penetration -> 20 Lethality - Level 1-18 Range: 8.75 -> 20 - Evens out with current values at level: 18

Duskblade of Drakthar: Currently 10 Armor Penetration -> 20 Lethality - Level 1-18 Range: 8.75 -> 20 - Evens out with current values at level: 3

So while Duskblade makes out like a bandit Youmuu's is obviously getting the short end of the stick, it does not even surpass live values at any point in the game.

So what's the point of all of this? The point is that Lethality is not NECESARILY stronger than flat armor penetration at any point in the game, it is simply an alternate way to calculate armor penetration so that it will scale with levels. If we really want to understand the potential value of Lethality and how effective it might be as opposed to flat armor penetration we are going to have to take more into account than simply 'weak early, strong late'.

Specifically here are a few things to keep in mind if we want to try to understand how effective lethality will be: How much Lethality is being given in comparison to current armor pen values? What level (if any) does lethality equal in power to current armor pen values? How much raw Lethality will a player be able to accumulate in comparison to flat armor penetration? (Btw, the answer to that last one is generally going to be about 50 armor penetration and 75 lethality)

As a final note, it will of course come to play testing to see how everything pans out. But since armor itself is not undergoing any noticeable changes we should be able to infer some things about how well Lethality will play out since we already have such a good comparison with the flat armor penetration of today. So when looking at changes to the PBE over the next few months just keep some of this in mind when thinking about how Assassins might be building in the coming season and how the scaling value of Lethality might effect their power curve throughout the game.