New accounts can affect your credit score in a few different ways, so opening a new credit card before applying for a mortgage could be detrimental. A new hard inquiry will cause an initial dip on your credit score, for starters. In addition, a new credit account will cause a drop in your average age of accounts. You’ll also see a decreased score due to the “new credit” FICO category, which counts for about 10% of your score. Then, if you carry a balance on that new account, you’ll also have an increased debt-to-income (DTI) ratio, which lenders factor into their decision process.