In League of Legends, most AP items are all about making your abilities deal more damage. Flat magic penetration, percentage one, AP, damage amplification, all of these stats are about achieving one same result through different means. Which means that for one given situation, one of them will always be strictly better than the rest with the other choices being wrong.

And yet most of us pick our AP items based on what feels right, while there is a best option. To stop doing that, here’s a guide to precisely explain when to buy AP, and when to buy magic pen - to deal more damage in your games without doing any further effort than reading a few paragraphs!

Second Item Choice

Most AP champions have specific needs for their first items (for most of them, that’ll be mana), so the real question isn’t asked until the second slot.

In Season 2024, there are three AP items that give nothing but damage: Rabadon’s Deathcap, Void Staff, and Shadowflame. So, we’ll compare these three.

For most champions, Shadowflame deals the most damage as a second item against enemies that haven’t bought any magic resist. Deathcap is the better option for champions whose AP scalings are exceptionally high compared to their base damage (Leblanc, for example). However, these two items are always extremely close (the better option never being more than 3% better).

On the other hand, Void Staff becomes better against anyone with at least a Null-Magic Mantle. While the exact threshold differs based on the champion’s scalings, it always remains under 25 bonus magic resist. And the more MR an opponent buys, the better Void Staff becomes.

Interestingly, these choices don’t change whether you’ve bought Sorcerer Shoes or not!

Warning - Exception for Mejai’s Soulstealer! Mejai’s is an item that we don’t count as a regular option since buying it depends on how the game goes. But if you have a fully stacked Soulstealer on top of your first item, Rabadon’s becomes better than Shadowflame in almost every case.

With Mejai’s, Void Staff will also then need more magic resist to burn through in order to outperform Deathcap, and the threshold will be much more versatile based on the user’s ratios. For the average mage, the cutoff will be at 72 MR, but it can vary anywhere between 61 and 105, being higher for champions with better AP scalings.

Third Item Choice

Now, let’s say you’ve bought Shadowflame as your second item. What should you get next - Rabadon’s, Void Staff, Horizon Focus, or Stormsurge for even more flat pen?

Here, Void Staff quickly becomes better. It deals more damage against all champions that have bought any sort of magic resist, and in most cases, it’s also better against melee opponents even if they haven’t bought any defensive item, as their base MR is higher.

Deathcap does have a slight edge against targets with low base magic resist and none purchased. However, the two items perform very similarly against anything that has less than 100 MR.

And all other options are worse in every case!

Notes, Disclaimers, and Clarifications

The first two sections gave you everything you needed if you were just looking for quick answers. From now on, we’ll dive further into the details, and go over everything that has been overlooked for the sake of conciseness.

First off, I should clarify that all items have been weighed for their price. Cheaper items have been counted with extra AP corresponding to the cost difference. For example, by the time you could build Deathcap, you could instead buy Shadowflame as well as one Amplifying Tome for the same price, so Shadowflame was counted with an extra 20 AP for a comparison more relevant to in-game decisions.

Not everything is about damage. Utility in kits will usually be affected by AP only, with magic pen contributing nothing to it. So naturally, if you’re playing something like AP Janna (I’m not here to judge, only to help you be more efficient, at whichever endeavor you have in League), it’s on you to leverage how much you want to optimize the burst from your tornado and Zephyr, versus how much you value your shield and heal. AP also improves your waveclear whereas magic pen does not, which may matter.

Additionally, items like Stormsurge, Horizon Focus, and Cryptbloom are slightly worse versions of our three aforementioned options - when it comes to damage. But they all bring utility and/or stats that aren’t just damage (movement speed, ability haste). This guide is here to help you understand what deals the most damage, not to state that Deathcap, Shadowflame, and Void Staff are the only three items you can pick from.

Not all damage is equal. Dealing 10% more damage to a tank and dealing 10% more damage to a carry don’t hold the same weight. We stated that Void Staff overperforms Shadowflame against enemies who have bought magic resist, but the fact is that each game will have you face champions both with and without MR. You’ll have to take your role in the game into account to determine which targets will be more important to damage for you.

Some aspects of a kit can’t be easily quantified. Ryze has mana scalings, Ahri has part of her damage become true damage, Evelynn ignores a percentage of the target’s resistances, Dr. Mundo has damage scaling with his opponent’s health (I did not insinuate that the question of AP versus magic pen applied to Mundo. I didn’t insinuate the opposite either. And I am not responsible for what decisions one might take after reading this guide).

All particularities like that can’t be easily calculated, so it’s best to keep in mind how they tip the scales. True damage makes AP slightly more valuable than all forms of magic pen compared to the norm, while reducing the opponent’s magic resist increases the value of flat magic pen over that of the percent-based one.

Note that magic resistance cannot be reduced below 0. So, over all the things we’ve said, always avoid accumulating magic penetration to a point where part of it will be wasted (including whatever magic resist reduction your champion’s kit might include).

The average mage has around 100% AP scaling for every 380 base damage at level 13. So if you want to calculate something for a specific champion, have that in mind to know whether their AP scaling is above or below the average!

Closing Out

This should give you a solid idea of when you should buy AP and when you should instead opt into magic pen. Another important fact to take away from this guide is that it isn’t just important to know the math behind which AP item to build, it’s also doable and accessible to calculate by yourself if you want to get to theorycrafting by yourself!