Jax benefits greatly from items that have both Ability Power and Attack Damage such as Guinsoo's Rageblade and Hextech Gunblade.
Jax can Leap Strike to friendly units, including wards. You can use them to plan your escape.
Karthus can cast spells for a short duration after he is killed. Move away from his corpse to be safe.
Make sure you always have enough health to survive Requiem, even if you have to go back to the base more frequently to heal.
The stats shown here show several significant Jax against Karthus counter stats that can help us realize the differences and similarities between the pair. Jax’s KDA ratio ([kills + assists] / deaths) of NaN is more than Karthus’s KDA ratio of NaN, indicating that Jax may be more central to his team's team fighting effectiveness than Karthus..
Jax normally has a similar longest killing spree as his opponent does. On average, he takes more damage than Karthus. This often reflects differing health capacities, yet it can also indicate that the one champ has less agility and thus is unable to escape additional damage when poked or engaged.
Both League champs are great champions. Both have their strengths, weaknesses, and counters. In League's current meta, Jax usually wins when taking on Karthus, with a 52.0% win rate. Therefore, Jax makes a good counter to Karthus.
While Jax does have a higher winrate compared to Karthus, when on opposite teams, Jax also has a lower learning curve that makes him a less complex character to pick up and master. You should be careful when picking Jax into Karthus.
Additionally, Jax has some amount of CC and other utility, a similar amount to Karthus. This often makes her just as valuable during team fights, especially when trying to counter champions with a lot of burst damage.
While there is not a single best champion overall in League of Legends, in Jax vs Karthus matchups, Jax is the better champ with a higher win rate, less champion complexity, and a similar amount of utility to help out your team members during team fights.
Jax is a decent counter to Karthus. Make sure you focus your actions on maximizing your CS and destroying objectives. If you can do that, you should do very well as Jax against Karthus.
If you would like to learn all of the intricacies of Jax in order to counter Karthus during both the early game and mid / late game phases of League of Legends, you should continue reading to learn a few extra lessons on this matchup. If you pay attention to the build and tips presented here, you will increase your win rate significantly and be closer to League of Legends pro players.
Jax most often picks up a similar amount of CS as Karthus. Champs who typically don't earn many minion kills often don't have to have much CS to be effective, such as sup champs. They are able to scale properly off of their abilities and first items alone. Yet, champions with large amounts of CS, such as hyper-carries, typically have to have many items to be effective. In either case, try to do better than the numbers displayed on this page to do well.
The best items to focus on in your Jax versus Karthus build include Sterak's Gage, Trinity Force, and Titanic Hydra. When Jax combined at least these three items in his build, he performed much better vs Karthus than with most other commonly used item sets. In fact, Jax had an average winrate of 52.0% when playing against Karthus with these items in his kit.
To have the best probability of coming out on top against Karthus as Jax, Jax players should use the Lethal Tempo, Triumph, Legend: Alacrity, Last Stand, Cosmic Insight, and Magical Footwear runes from the Precision and Inspiration rune sets. Out of all the rune sets players picked for Jax vs Karthus counters, this combination of runes yielded the highest win rate. In fact, these runes provided a 52.0% winrate overall.
If you would like to see Jax vs Karthus tips and counter stats for a a specific division, feel free to select one from the selection menu provided above. If viewing for the first time, the statistics and build suggestions displayed are calculated using every match completed with these champions.