According to the National Priorities Organization:

In 2013, the cost of tax breaks was equal to the entire U.S. discretionary budget [1]. However, the discretionary budget is subject to an annual appropriations process, where Congress debates the proposed spending. Tax breaks, on the other hand, remain on the books until lawmakers modify them. As a result, over a trillion dollars a year in lost revenue – more than 1.6 times the 2013 budget deficit – goes largely unnoticed.