All characters who survive an adventure and return to safety gain experience points (XP) due to any treasure recovered or monsters defeated. Experience points are awarded by the referee (see Awarding XP).

Characters with especially low or high scores in their class’ prime requisites receive a bonus or penalty for XP earned (see Ability Scores). These modifiers are applied to the total XP gained by each character following an adventure.

When a character gains enough XP to reach the next experience level, the player should consult the description of the character’s class and note any improvements in saving throws, attack probabilities, spells per day, and other class abilities. If the character’s Hit Dice increases, a new Hit Die of the specified type should be rolled, adding the result to the character’s maximum hit point total.

Characters can advance up to one level in one session. Any additional XP that would take a character two or more levels above their current level is lost, leaving the character at 1 XP below the total for the next level.

In some campaigns, characters gain the right to bear specific titles as they advance in level. Such titles may be granted by the guilds, colleges, or temples that PCs are associates of. Level titles often vary significantly between campaign worlds, but the following lists may be used as inspiration:

Human character classes are listed as having a maximum level of 14. This range of levels presents the best play experience regarding challenge and reward. However, some groups may wish to continue playing at extremely high levels. This must be considered carefully, as demihuman PCs will be left behind due to their strict level limits. If the referee allows continued play into higher levels, the following guidelines—allowing human characters to advance to a maximum of 36th level—may be used.

Clerics require an additional 100,000 XP per level beyond 14th and gain 1 hit point per level gained. Spells of higher levels become available as the character advances.

Fighters require an additional 120,000 XP per level beyond 14th and gain 2 hit points per level gained. Fighters of 20th level may make two attacks per round. This increases to three attacks per round at 25th level and four per round at 30th level.

Magic-users require an additional 150,000 XP per level beyond 14th and gain 1 hit point per level gained. Spells of higher levels become available as the character advances.

Thieves require an additional 120,000 XP per level beyond 14th and gain 2 hit points per level gained. Additional skills become available to high-level thieves, including the ability to climb upside down or horizontally, voice skills such as mimicry and ventriloquism, and other skills of deception.

See Wealth.

See Hirelings.