5.4 Deficits and the National Debt

A government budget deficit happens when tax revenues fall short of government purchases plus transfer payments in a year, and a surplus is the opposite. Every deficit gets added to the national debt, and once a government owes that debt, it has to pay interest on it, which means less money left for other uses.

Why This Matters for the AP Macroeconomics Exam

This topic gives you the vocabulary and cause-and-effect logic that show up across Unit 5. You need to define a budget deficit and surplus precisely, connect deficits to a growing national debt, and explain the burden that interest payments create. This reasoning sets up the next topic, crowding out, where government borrowing to cover deficits affects the loanable funds market and the real interest rate. On the exam, expect to define these terms, explain the long-run consequences of running deficits, and trace how borrowing today affects future spending choices.

more resources to help you study

practice multiple choiceFRQ practice & scoringcheatsheetsscore calculatorAMSCO guided noteskey terms

Key Takeaways

• A budget surplus means tax revenues are greater than government purchases plus transfer payments in a given year; a deficit means tax revenues are less.
• A government adds to the national debt every year it runs a deficit, and it can pay down debt with a surplus.
• The national debt is the accumulation of past deficits minus past surpluses.
• Governments must pay interest on accumulated debt, so the debt keeps growing through interest even without new spending.
• Interest payments are an opportunity cost: that tax revenue cannot fund other programs or tax cuts.
• This logic connects directly to crowding out, where deficit borrowing pushes up real interest rates.

Budget Surplus and Deficit

The federal budget is the projection of all government spending and revenue over a 12 month period. The fiscal year begins on October 1.

A government budget surplus occurs when tax revenues are greater than government purchases plus transfer payments in a given year. The government spent less than it received, and that excess can be used to pay down the national debt.

A government budget deficit occurs when tax revenues are less than government purchases plus transfer payments in a given year. The government spent more than it took in.

The basic formula to keep in mind:

Budget balance = Tax revenues - (Government purchases + Transfer payments)

If the result is positive, that is a surplus. If it is negative, that is a deficit.

As an application, the U.S. government has run a budget deficit in most years since 1969, with only a few surplus years during that stretch. This is an illustrative example, not required AP content, but it shows how common deficits are in practice.

The National Debt

The national debt is the total amount the federal government owes from borrowing to cover past budget deficits, minus any past surpluses used to pay it down. Think of the deficit as a single year's gap and the debt as the running total of all those gaps over time.

Unlike a household, the federal government can keep borrowing over time, so it does not need to pay off the entire debt at once. The debt still matters, though, for one main reason: interest.

How Deficits Add to the Debt

When the government runs a deficit, it borrows to cover the gap between revenues and spending, and that borrowing is added to the national debt. When it runs a surplus, it can use that money to pay down some of the debt.

So the chain works like this:

1. Government spends more than it collects in a year (deficit).
2. It borrows to cover the gap.
3. That borrowing increases the national debt.
4. The larger debt requires larger interest payments.

The Burden of the Debt

A government must pay interest on its accumulated debt. This is the core burden the AP exam wants you to explain.

Two things happen as debt grows:

• The interest payments themselves add to the debt, so the debt can grow even without new program spending.
• Those interest payments use tax revenue that could otherwise fund programs like education, infrastructure, or defense, or be used to cut taxes.

That second point is an opportunity cost argument. Every dollar spent servicing the debt is a dollar that cannot be used for something else.

How to Use This on the AP Macroeconomics Exam

Free Response

Be precise with definitions. If a question asks you to define a budget deficit, name both sides of the comparison: tax revenues versus government purchases plus transfer payments. A vague answer like "spending more than you make" may not earn the point.

When you explain the burden of the debt, do not stop at "the debt is big." Explain the mechanism: deficits add to the debt, the government pays interest on that debt, and those interest payments are funds that cannot be used elsewhere. Walk through each step rather than jumping to the conclusion.

Common Trap

Watch the difference between the deficit and the debt. The deficit is a flow measured over one year. The debt is a stock that accumulates over many years. A government can reduce its deficit and still add to its debt as long as it is still running any deficit at all.

Connecting to Crowding Out

If a free-response prompt moves from deficits into the loanable funds market, you are heading into crowding out. The link is that the government borrows to finance a deficit, which increases the demand for loanable funds and raises the real interest rate. Keep that chain ready because deficit questions often lead there.

Common Misconceptions

• A deficit and the debt are not the same thing. The deficit is the one-year gap between revenue and spending. The debt is the total of all past deficits minus past surpluses.
• Running a smaller deficit does not pay down the debt. As long as there is any deficit, the debt is still growing. You only pay down the debt with a surplus.
• The government does not have to pay off the entire national debt at once. Unlike a household, it can keep borrowing and rolling over debt over time.
• Interest payments are not optional. A government must pay interest on accumulated debt, and skipping those payments would risk default.
• The burden of the debt is mostly about opportunity cost, not just the size of the number. The real concern is that interest payments crowd out other uses of tax revenue.

Related AP Macroeconomics Guides

• 5.1 Fiscal and Monetary Policy Actions in the Short-Run
• 5.2 The Phillips Curve
• 5.5 Crowding Out
• 5.3 Money Growth and Inflation
• 5.6 Economic Growth
• Unit 5 Overview: Long-Run Consequences of Stabilization Policies