Deficit Drivers
The federal deficit is the gap between what the government spends and what it collects. Understanding that gap means understanding what drives each side.
The deficit is driven by two broad forces: the level and composition of federal spending, and the level and composition of tax revenue. In recent years, spending has consistently outrun revenue, and rising interest expense has added a third, self-reinforcing driver.
Total Spending (FY24)
~$6.9T
CBO estimate
Total Revenue (FY24)
~$5.1T
CBO estimate
Net Interest (FY24)
$880B
Growing driver
Spending
Mandatory vs. Discretionary
Federal spending is divided into two broad categories. Mandatory spendingis governed by existing law — eligibility rules determine how much is paid out each year with no need for annual appropriations. It is dominated by Social Security and the major health programs. Discretionary spending is funded each year by congressional appropriations; it covers defense, most domestic agencies, education, transportation and research.
Because mandatory spending grows on autopilot with an aging population and rising health costs, it is the largest structural reason deficits have become harder to close through annual budgeting alone.
Social Security
The largest single federal program, paying benefits to tens of millions of retirees, disabled workers and survivors. Its costs grow with the number of beneficiaries and long-run wage growth. Under current law, its trust funds are projected to be unable to pay full scheduled benefits in the coming decade without reform.
Medicare & Medicaid
Health programs are the fastest-growing part of mandatory spending. Medicare serves older and disabled Americans; Medicaid serves low-income households and is jointly funded with states. Growth is driven by enrollment and per-person health costs that have historically outpaced inflation.
Defense
The largest discretionary category, covering personnel, operations, procurement and research. Defense spending levels reflect strategic priorities and global commitments, and are set through annual appropriations.
Other Federal Programs
Income security, veterans' benefits, education, transportation, science and infrastructure, and the everyday operation of government. Individually smaller, together they account for a meaningful share of total outlays.
Revenue
Tax Revenue
Revenue comes overwhelmingly from three sources: individual income taxes, payroll taxes (funding Social Security and Medicare), and corporate income taxes. The remainder comes from excise taxes, customs duties and miscellaneous receipts. Revenue rises and falls with the economy and the tax code; changes in rates, deductions and brackets alter how much is collected at any given level of activity.
The Self-Reinforcing Driver
Interest Expense
Unlike program spending, interest is not a policy choice — it is the mechanical consequence of the debt and prevailing rates. As both have risen, interest has become one of the largest items in the budget, and the government effectively borrows to pay it. That creates a feedback loop: higher debt can raise borrowing costs, which raises interest, which raises debt further.
References