My impression has been that the income is definitely used to determine the amount of credit they're willing to issue you, but not necessarily whether to approve you. "Income" is fairly ambiguous for me, and I choose to use a much higher number than, say, the IRS definition. I do try to be consistent about what I say though. Chase now asks me as a final step if I'm sure there isn't more income I want to claim. I say no, and it doesn't auto approve. It always comes through a few days later, after they've lowered the credit limit on another card to give to the new card.