it isn't a matter for the difference, if you are married you have to file that way
filing jointly will cause your combined income to reach a higher tax bracket possibly
is this a test to see if you want to get married?How much are taxes decreased when you get married versus single?
Assuming that both of you are making roughly the same amount of money and don't have any children, your tax bill won't be affected by getting married.
If your incomes are fairly lopsided you may save a few dollars in tax when you get married if you file a joint return.
If you each have one or more children and are both filing as Head of Household and are claiming the EIC at nearly the maximum amount, getting married could easily cost you thousands in added taxes and lost refundable credits. In the worst case scenario the hit can be well over $10,000.