I opened the card in 1996 with a 2500 credit limit, right now it sits at $45K, I never asked for an increase, I seemed to get one about once every 16 months until it hit that number in early 2019, hasn't moved since. My usage is very predictable: I max out the bonus category every single quarter plus a random few regular charges just to keep the card active outside of just bonuses. This means the monthly bill is hardly anything to write home about, so I'm not sure what triggered the increases.