US National Debt Hits $40 Trillion as Interest Costs Raise New Market Risks

Overview

The US national debt has surpassed $40 trillion for the first time, raising alarms about increasing interest expenses, substantial Treasury issuance, and the long-term viability of federal finances. As of August 18, the total public debt outstanding was approximately $40.047 trillion, comprising about $32.266 trillion in debt held by the public and $7.782 trillion in intragovernmental holdings.

Key Takeaways

• Total US federal debt reached $40.047 trillion, with $32.266 trillion held by the public.
• The national debt increased by approximately $2.9 trillion over the past year, averaging nearly $8 billion per day.
• The Congressional Budget Office (CBO) anticipates net interest spending to exceed $1 trillion in fiscal 2026.
• Growing Treasury supply and rising interest costs could exert pressure on bond prices, equity valuations, and private-sector borrowing.

Debt Growth and Economic Impact

The $40 trillion figure represents gross federal debt, which includes securities owned by various entities. The portion of debt held by the public is particularly significant as it reflects the government's borrowing from financial markets. The Joint Economic Committee reported that the national debt increased by $2.88 trillion in the year leading up to August 7, translating to an average increase of $7.91 billion per day.

Factors contributing to this increase include persistent budget deficits, rising costs for Social Security and Medicare, defense spending, and interest payments. Although emergency measures during the pandemic accelerated borrowing, the trend has continued post-pandemic.

Interest Costs and Budget Constraints

The sustainability of the national debt is influenced not only by its size but also by financing costs, economic growth rates, and tax revenues. The average interest rate on marketable federal debt rose to 3.443% in July 2026, up from 1.476% five years prior. The CBO projects that net federal interest spending will reach approximately $1.04 trillion in fiscal 2026, which could rise to $2.14 trillion by 2036.

As interest payments grow, they limit fiscal capacity for essential services and create a compounding effect, necessitating additional debt issuance to cover existing obligations.

Market Reactions and Treasury Actions

The milestone of $40 trillion in debt coincides with rising Treasury yields, which have reached levels not seen since 2007. The 30-year Treasury yield hit 5.31%, while the 10-year yield approached 4.65%. These higher yields can restrict household spending and business investment, as they serve as benchmarks for various loans and credit.

In response to market conditions, the Treasury plans to double the maximum size of certain long-term bond buybacks to enhance liquidity in older securities. However, these buybacks do not reduce the national debt, as they are financed through new Treasury issuance.

Conclusion

While crossing the $40 trillion threshold does not immediately signal a funding or default crisis, the rapid accumulation of debt and the increasing share of federal revenue allocated to interest payments highlight the growing risks associated with fiscal policy for the economy and financial markets.