Why the $40 Trillion U.S. Debt Is More Exposed to Rate Shocks Than Japan’s

WASHINGTON — net interest payments on U.S. federal debt have reached $1.25 trillion a year, surpassing overall national defense outlays and becoming one of the fastest-growing items in the budget. The gross national debt crossed $40 trillion after the government borrowed at a pace of approximately $7 billion per day.

The U.S. debt-to-gross domestic product (GDP) ratio is approximately 126%, below Japan’s 207% and Singapore’s 172%. But economists say the way American debt is financed leaves the country more exposed to interest rate shocks and fiscal paralysis than some nations with higher ratios.

International Monetary Fund World Economic Outlook data show that the United States has the world’s largest sovereign debt stack, more than double China’s $18.7 trillion. Japan’s financial position differs sharply: roughly 90% of Japanese government bonds are held domestically by commercial banks, institutional pension funds, insurance companies and the Bank of Japan. The country also has the world’s largest Net International Investment Position, making it the leading foreign creditor nation.

Japanese households’ savings rate relative to GDP is roughly double that of U.S. households, providing a domestic liquidity buffer for government debt issuances. By contrast, the United States is the world’s largest net debtor nation, with a substantial portion of Treasury securities held by foreign sovereign and private investors, including central banks in Japan, China and the United Kingdom. That reliance on overseas capital exposes U.S. bond markets to international capital shifts, currency swings and global interest rate movements.

“Japan’s debt dynamics are fundamentally different from those of the United States,” Jack Salmon, a research fellow at the Mercatus Center at George Mason University, noted in a financial analysis. “Japan is the world’s largest creditor nation. The U.S. is the world’s largest debtor.”

The growing interest bill is also narrowing Washington’s room to respond to a downturn. In past recessions, the Federal Reserve cut benchmark rates while Congress authorized debt-financed stimulus, including tax cuts and infrastructure spending. With debt at $40 trillion and interest costs consuming a growing share of federal revenue, large-scale discretionary stimulus is more constrained.

“The U.S. has never entered a recession with this little fiscal buffer,” Apollo Global Management Chief Economist Torsten Slok said. He added that the standard playbook of rate cuts, falling Treasury yields and expansionary fiscal policy faces hurdles when the sovereign issuer is already fiscal-stretched. Aggressive spending can increase the supply of Treasury bonds, pushing long-term yields and borrowing costs higher. Rapid Federal Reserve easing, meanwhile, risks reigniting inflation and weakening demand among foreign and domestic institutional buyers for long-duration fixed-income securities.

Some academic economists question debt-to-GDP as a measure of fiscal health because it does not account for assets, balance-sheet structures or revenue capacity. Jonathan Berk, a professor of finance at the Stanford Graduate School of Business, said dividing a nation’s accumulated debt by one year of GDP is equivalent to dividing a homeowner’s remaining mortgage balance by one year of rental income. The calculation omits state-owned assets, tax collection authority, natural resources and private wealth reserves that support sovereign creditworthiness.

Even alternative measures show rising cost pressures. As older Treasury notes issued during periods of historically low interest rates mature, the Treasury Department must refinance them at current market rates, lifting the average interest rate across the national debt portfolio. Congressional Budget Office projections identify rising net interest expenses and mandatory Social Security and Medicare outlays as the primary drivers of future federal deficits. Under its baseline projections, debt held by the public is set to grow over the next three decades amid structural primary deficits and compounding borrowing costs; interest payments alone are projected to become the largest federal budget category, exceeding all discretionary programs combined.

In Japan, rising long-term yield obligations, currency volatility and imported energy inflation have prompted policymakers to raise domestic interest rates from historic lows, increasing the government’s debt-servicing costs and signaling limits to domestic debt expansion even in high-savings economies.