national average mortage rate percentage of income for mortgage What is a debt-to-income ratio? Why is the 43% debt-to-income. – The 43 percent debt-to-income ratio is important because, in most cases, that is the highest ratio a borrower can have and still get a Qualified Mortgage. There are some exceptions. For instance, a small creditor must consider your debt-to-income ratio, but is allowed to offer a Qualified Mortgage with a debt-to-income ratio higher than 43 percent.