The Pew Research Center last week broke down how federal dollars are spent. The vast majority of spending is on social-insurance programs such as Social Security, Medicare and Medicaid:
When thinking about federal spending, it’s worth remembering that, as former Treasury official Peter Fisher once said, the federal government is basically “a gigantic insurance company,” albeit one with “a sideline business in national defense and homeland security.” In fiscal year 2016, which ended this past Sept. 30, the federal government spent just under $4 trillion, and about $2.7 trillion – more than two-thirds of the total – went for various kinds of social insurance (Social Security, Medicaid and Medicare, unemployment compensation, veterans benefits and the like). Another $604 billion, or 15.3% of total spending, went for national defense; net interest payments on government debt was about $240 billion, or 6.1%. Education aid and related social services were about $114 billion, or less than 3% of all federal spending. Everything else – crop subsidies, space travel, highway repairs, national parks, foreign aid and much, much more – accounted for the remaining 6%.
Additionally, writes Pew:
Measured as a share of GDP, the biggest long-term growth in federal spending has come in human services, a broad category that includes various kinds of social insurance, other health programs, education aid and veterans benefits.
...Besides human services and national defense, the next-biggest category of federal spending is interest on public debt. Excluding interest paid to government trust funds (such as the Social Security and military-retirement trust funds) and various other small government loan programs, the $240 billion in net interest paid on federal debt in fiscal 2016 represented 1.3% of GDP.
You can read Pew's blog post here.