So, I have a problem, and I'm a bit surprised that no one else has posted about it yet. This is a question about everyone's darling, the Leadership feat.
From the PRD:
Cohort Level: You can attract a cohort of up to this level. Regardless of your Leadership score, you can only recruit a cohort who is two or more levels lower than yourself. ...
A cohort does not count as a party member when determining the party's XP. Instead, divide the cohort's level by your level. Multiply this result by the total XP awarded to you, then add that number of experience points to the cohort's total.
If a cohort gains enough XP to bring it to a level one lower than your level, the cohort does not gain the new level—its new XP total is 1 less than the amount needed to attain the next level.
... Don't consult the table to see if your cohort gains levels, however, because cohorts earn experience on their own.
So, what am I supposed to do if I don't use XP at all? I use the milestone level system, as I think, honestly, most Pathfinder players do these days, and it's downright weird that the book doesn't have an explicit clarification for that extremely common playstyle.
The most obvious answers are probably just, "level them up whenever the PC levels up", or "level them up whenever the PC's Leadership score increases".
The latter seems potentially problematic, since Leadership Scores can shift wildly in response to story events and new gear (whoops, I spent a day wearing my Headband of Charisma, time for a level-up for the cohort!). Of course, the PC could just ditch the old cohort and get a new one who's more properly capable, so maybe basing it off the Leadership score is appropriate.
What do you think?