From Intuit:

“The three biggest categories of expenditures are:

Major health programs, such as Medicare and Medicaid

Social security

Defense and security

Interest on the national debt and various safety net programs such as low-income assistance comprise a sizable chunk of national expenditures, while other categories such as transportation and infrastructure spending round out the government budget.”

Entitlements (social security and Medicare) make up the largest item, and have been projected to cripple the US economy due to projected eligibility growth.