National Debt: How Governments Borrow, Spend, and Why It Matters

The Number Politicians Invoke and Few Understand

As of early 2025, the United States national debt exceeded $36 trillion. This number appears in political speeches, campaign ads, and news coverage as a self-evident indicator of fiscal irresponsibility, national weakness, or impending crisis. What it actually means — who is owed this money, under what conditions it becomes problematic, and what policy choices could or should follow from it — is considerably more complex than the raw number suggests.

Japan's national debt exceeds 260% of GDP. The United States sits around 120%. The UK is approximately 100%. These nations retain high credit ratings and have not faced debt crises. Argentina, with a debt ratio far lower than Japan's in some periods, has defaulted multiple times. The number matters. But what matters more is the structure of the debt, who holds it, in what currency it is denominated, and at what interest rate it is financed.

What National Debt Actually Is

National debt is the accumulated total of all past government borrowing that has not yet been repaid. Each year a government runs a deficit — spending more than it collects in taxes — it must borrow the difference. This borrowing accumulates into the national debt.

The U.S. national debt has two components:

• Debt held by the public — Treasury securities (T-bills, notes, bonds, TIPS) held by individuals, institutions, foreign governments, and the Federal Reserve. This is the economically meaningful component — approximately $27 trillion as of early 2025 — representing real claims by external holders on future government payments.
• Intragovernmental debt — IOUs owed by one government account to another. The largest component is the Social Security Trust Fund, which has accumulated a surplus invested in special Treasury securities. These are internal accounting entries; the government effectively owes money to itself.

When public discussion refers to the national debt, it typically means the gross debt (both components combined), which can overstate the economically meaningful external obligation.

How Governments Borrow

The U.S. Treasury raises money by issuing securities at regular auctions. Major categories:

At Treasury auctions, primary dealers (major financial institutions) and other bidders compete for securities. Interest rates are determined by the competitive bidding process. The Federal Reserve does not directly purchase at primary auctions but buys and sells existing Treasury securities in the secondary market as part of monetary policy operations.

Who Holds U.S. Debt

The composition of U.S. debt holders is frequently misrepresented. Popular accounts sometimes suggest China or other foreign governments "own" most U.S. debt and therefore hold dangerous leverage over American policy. The actual distribution is quite different:

The largest single holder is the Federal Reserve, which accumulated Treasuries through successive rounds of quantitative easing. Most U.S. debt is held by American investors and institutions. China's holdings, while large in absolute terms, represent a modest share of total debt and have actually been declining as China has diversified its reserves.

When Does Debt Become a Problem?

There is no universally agreed threshold at which national debt becomes dangerous. Economists Carmen Reinhart and Kenneth Rogoff's influential 2010 paper claimed to find that growth slowed sharply when debt exceeded 90% of GDP — a finding that became politically significant. A 2013 reanalysis by Thomas Herndon, Michael Ash, and Robert Pollin identified data errors in the original paper that substantially changed the results; the relationship between debt and growth was found to be much weaker than Reinhart and Rogoff reported.

The relevant considerations for whether debt is problematic include:

• Interest costs as share of revenue — When interest payments consume a large fraction of government revenue, less is available for other priorities. As of 2024, U.S. net interest payments approached $900 billion annually, making it one of the largest items in the federal budget.
• Currency denomination — Debt denominated in one's own currency (like U.S. Treasuries) cannot trigger the kind of sudden stop that affects countries borrowing in foreign currency. Argentina's crises involved dollar-denominated debt; the government ran out of dollars, not pesos.
• Growth vs. interest rate differential — If the economy grows faster than the interest rate on debt, the debt-to-GDP ratio falls automatically even with moderate deficits. For much of the post-2008 period, interest rates were below growth rates (r < g in economists' notation), making the debt dynamics more benign. The post-2022 rate increases shifted this relationship, making deficits more costly.
• Investor confidence and reserve currency status — The U.S. benefits from the dollar's reserve currency status, creating persistent global demand for Treasuries that allows the U.S. to borrow at lower rates than other countries would face at similar debt levels.

The Generational Equity Debate

A common argument against deficit spending is that it passes costs to future generations — children will repay today's debt. The argument is partially correct and frequently overstated.

When a government sells bonds to domestic holders, the future interest payments are transfers from future taxpayers to future bondholders — both groups within the same future generation. The net generational burden is the reduction in future productive capacity that results from borrowing crowding out private investment. If government borrowing displaces productive private investment (in equipment, R&D, education), future generations have less capital and lower productivity. If government spending goes toward investments that enhance future productivity (infrastructure, research, education), the generational calculus is more favorable.

Debt held by foreign creditors does represent a more direct future cost — future generations will send real resources abroad to service it. But even this is modulated by whether the borrowed resources were invested in ways that increased future productive capacity beyond the debt service obligation.

National debt numbers, by themselves, answer almost none of the questions that matter for fiscal policy. What the debt financed, at what cost, held by whom, in what currency, in what economic environment — these factors determine whether a given debt level represents a serious problem or an ordinary feature of sovereign fiscal management.