Party size penalty

If a party consists of more than one character, an experience penalty is incurred. The larger the party, the more severe the penalty. All PCs, henchmen, familiars, animal companions, summoned creatures, dominated creatures, etc. count towards the party size when determining this penalty. Because of this, it may not always be worth the additional XP penalty to make use of support characters, although henchmen in particular may be entertaining to keep around for roleplaying purposes.

The exact mechanics of the penalty appear to be as follows: Any XP received from kills will be multiplied by the party size penalty factor. (It is independent of any multiclass penalty, thus the combined penalty is the product of the two.) KillXP = BaseXP * MulticlassPenalty * PartySizePenalty The party size penalty is determined by the formula: PartySizePenalty = 4 / (3 + PartySize) So if you're completely solo, the party size penalty is (4/4) = 1.0 (ie, there is no penalty), whereas if you have summoned a familiar, the party size penalty is (4/5) = 0.8.