Experience Points

Experience Points (or XP for short) are a measurement of character progress. The player character can earn experience points for killing creatures and solving quests. They are used to determine when a character should gain a new level. Different amounts of experience points are awarded for killing more dangerous creatures. For example, in Fallout 3, killing a deathclaw nets 50 experience points while killing a radroach gives only 1. Experience points can also be gained for disarming mines and traps, picking locks, hacking computers, passing speech challenges, doing sections of a quest and, in Fallout: New Vegas, completing passive challenges like killing a set amount of an enemy. The number of experience points earned for an accomplishment are not dependent on character level.

Fallout
XP in Fallout is a conventional type similar to Dungeons and Dragons where levels are separated by a large amount of experience. For example, it takes 1,000 XP to reach level 2, 3,000 for level 3, 6,000 for level 4, and so on.

Fallout 2
Fallout 2's XP system is similar to Fallout's. The only major difference is that leveling requires more XP than in Fallout.

Fallout 3 difficulty modifier
Changing the difficulty level will also change the experience gained from killing enemies. Playing on Very Hard instead of Normal makes a kill worth 50% more experience, while playing on Very Easy makes it worth 50% less. For example, a deathclaw is worth 25 XP on Very Easy, 50 XP on Normal, and 75 XP on Very Hard.

The additional experience from fights on Very Hard compared to Very Easy is somewhat compensated by the enemies being much tougher. In the end, the player's skills and play style determine which difficulty setting allows for optimal leveling.

XP caps at level 20 on all difficulties without the Broken Steel add-on, which increases the cap to 30.

Fallout: New Vegas
Fallout: New Vegas does not reward XP based on the level of difficulty selected, despite the manual (PC and X360 version) stating otherwise. This somewhat alleviates the stress encountered while playing the game simultaneously on Hardcore, as it is not necessary to play it on Very Hard.

Unlike Fallout 3, Fallout: New Vegas awards XP for kills made by followers. This increases the usefulness of followers and significantly reduces the hassle of having to compete with them for XP.

Fallout 4
The higher the Sole Survivor's Intelligence, the more experience points they earn.

The Idiot Savant perk offers significant XP increases. The higher the Intelligence, the lower the chance of activating the perk.

Similar to New Vegas, Fallout 4 also awards experience points for kills made by a follower. However, the player must get in at least one hit before the follower makes the kill in order for the experience points to count.

In Survival mode, enemies that are killed by the Sole Survivor yield twice as much experience. This is the first time since Fallout 3 where a higher difficulty means more experience gain.

Fallout Tactics
XP in Fallout Tactics are given to all party members, regardless of the number of members. The game does not feature difficulty modifiers; however the Tough Guy game mode can provide 100% XP bonus (30% in versions prior to 1.27).

Bugs

 * Earning experience points and dying or loading an older save right before they register yields the points in the older save.
 * This appears to only be a display issue as the points are not added to the total on either platforms, this is easily realized if the player would have gone up a level.
 * It is possible to earn XP past where a level-up should happen without the game registering the level-up. This results in being stuck at level one. The XP counter may end up reading something like 600/200, indicating that a level-up should have happened 400 XP "ago". This may happen at any level or only from the start of the game. If it happens at the start of the game, beginning a new game fixes this bug, so watching the XP meter closely is a good idea.
 * Upon starting a new character, the game will recognize the level 1 character as a continuation of the most recent save (typically a level 30 character). This will make the player unable to level up at some point. This can be fixed by deleting all the save files and starting a new game.
 * This can also be solved by following these steps:
 * Start a new game on a different profile that has no save file from the game.
 * Go to memory under system settings and delete the most recent auto save from the bugged profile.
 * Start a new game, and the bug should not occur. If it does, try the same process but exit the town before 200 XP is reached.
 * If a single accomplishment results in enough experience to level up twice, the game will register two level-ups but will not award additional skill points. E.g., if the 1000 XP for completing the quest "Ring-a-Ding-Ding!" would result in going from level 6 to level 8, the skill points that would result from attaining level 7 are lost.
 * Fixed in a recent patch.

Erfahrungspunkte Points d'Expérience Punkty doświadczenia Очки опыта puntos de experiencia