I find that about 1/3 of the time, right around the 4 or 5 month mark on a new card, I will get an unsolicited credit line increase, usually around $3000. I also find that if I keep a card long term with steady spending, roughly every 2 years, I'll get a similar unsolicited increase.

I am in the habit of proactively lowering my credit lines in advance of new applications, so I assume that factors in, as I always have excess credit line available in Chase's viewpoint.