Aptitude is a term represented by a percentage for each character. Every base stat has an aptitude for every character. This aptitude alters the bonuses from equipment by that percentage. For example, Adell has an aptitude of 130% for his HP. If he equips a weapon that increases that stat by 100, then he would instead receive a bonus of 130.

Aptitude is only one of the factors that affects the stat bonuses granted by items. Item rarity can also affect item bonuses, and weapon mastery increases stat bonuses granted by weapons. In Disgaea: Hour of Darkness and Disgaea 2: Cursed Memories, Aptitudes go up by multiples of 10%. In Disgaea: Hour of Darkness, all storyline characters (with a few exceptions) and monsters (except the Galactic Demon) have 100% aptitudes across the board.

Every character and class has their own aptitude levels. These can be found on each of the individual class or character pages. In general, higher tiers of the same class have a greater aptitude than their lower tier counterparts. For example, in Disgaea 2, tier one of the Knight class has an HP aptitude of 80%, while tier 4 of the same class has an aptitude of 90%.

Unique characters such as Laharl have their own aptitudes apart from other classes, which are generally similar in magnitude to those of the best classes. In Disgaea 3: Absence of Justice and Disgaea 4: A Promise Unforgotten, each time a unique character such as Mao transmigrates, they gain a permanent 5% bonus to all of their aptitude values. This bonus can be applied a maximum of 5 times for each such character.

Also, in Disgaea 3 the Class World allows players to add further increases to the aptitudes every time they run through a character's world. This allows players to have their characters reach aptitude limits that were unheard of in previous Disgaea games (such as having Laharl's Attack Aptitude reach 200%). Characters can raise their aptitudes by a maximum of 100% each, 255% for characters with a base aptitude of 155% or more. The Class World will increase aptitudes after clearing 10 floors. The amount of aptitude points varies in each run and they are distributed randomly.

In Disgaea 4, you can enter the Chara World to allow players to further increase a character's aptitude to 300%. Like in Disgaea 3, after clearing 10 floors in Chara World, the host character will gain aptitude points that are distributed randomly.

In Disgaea D2, Aptitudes can be increased to 300% by the use of the Devil Dojo. Generic characters will now also gain Aptitude bonuses for reincarnating like Unique characters do.

In Disgaea 5: Alliance of Vengeance, players can use the Chara World like in Disgaea 4 to increase a character's aptitudes. In this Chara World, aptitudes can only increase by up to 5% per stat per Chara World Session. However, upon reaching the "Goal" space, one of the available rewards is a further 5% increase. Aptitudes are increased in the Chara World via special squares or defeating a shadow heart. There are also several aptitude-increasing Evilities. Additionally, reincarnating a character increases that character's aptitudes by 5%, up to five times per character.