As you've probably already noticed from looking at your credit card application, federal rules require lenders to approve or deny your new account based on your ability to repay your debt. Under regulations imposed by the Credit CARD Act, banks must ask about your individual income, not your household income. What you answer on your credit card application should match the data already showing up in your credit report. Therefore, even if you and your wife split your mortgage payment down the middle, you'll still want to list the entire payment.
That's because your prospective credit card issuer uses information from your credit report to verify both your identity and your disposable income. All three credit bureaus supply banks with algorithms that estimate your income based on your current debts and on the consumer trends in your neighborhood. Banks don't have to do this -- the law requires them to make the best decision based on the information you report. Yet, news reports indicate that income estimation tools have become commonplace among lenders who want to minimize their risk in the wake of last decade's credit crunch.
If you list just the portion of the mortgage that you pay on your own, you run the risk of raising a red flag based on your previous credit reports. For instance, if you and your wife contribute to a regular $1,000 payment, that's the amount that shows up on both of your files.
The consequences of providing a different answer vary by lender. For instance, an automated instant approval offer may decline you immediately because a bank's system can't reconcile your response with credit bureau records. A more flexible lender may send your application for manual review, enabling an account representative to make a judgment call based on your overall situation.