Ben Miller's answer is certainly accurate, but there's another angle that you should be made aware of.
Under the 2013 amendment (PDF) of the federal regulations regarding the Credit Card Act of 2009, persons 21 and older may report their total household income as their own personal annual income on a credit card application, provided that they have a reasonable expectation of access to household funds.
In other words, you may combine the annual income of yourself and your spouse / partner / significant other with whom you share a household if you typically share household expenses and expect that the other person would help pay your debts if you were unable to pay on your own. In fact, you may both use the combined total on all of your credit card apps. You don't need to disclose the fact that you are reporting total household income -- this is your right under federal regulations. Note that a credit card application may explicitly tell you not to include income of another member of your household as income -- this is allowed by regulation -- and in that case you would only list your own income . . . or pick a different credit card to do business with!
The rationale behind this amendment is that it affords equal credit treatment to both parties when one works outside the home and one is primarily a stay-at-home parent.