Although your income might be in the 15% tax bracket our tax system is a graduated taxing system so everybody pays zero tax on some income and 10% on some income then 15% etc etc. So you're blended rate is what the program is showing you. Since you must be using the downloaded version of the program switch to the forms mode and look for the worksheet that shows how the taxes were calculated. If you had qualifying dividends and or long-term capital gains then you're being taxed at a lower rate so look for the capital gains worksheet.
