U.S. — The Penn Wharton Budget Model has defined a federal debt solvency limit at a debt-to-GDP ratio exceeding 210%. The economic research organization stated that above this threshold, future tax revenue would be insufficient to cover interest payments, even with feasible taxes on labor income, at returns acceptable to investors. The model added that beyond this limit, defaulting on Treasury debt or on inflation-adjusted pay-as-you-go transfers, such as Social Security, becomes a near certainty.

As of July 4, 2026, total U.S. debt is $39 trillion, with publicly held debt equivalent to the size of the entire U.S. economy. Annual interest costs on this debt amount to $1 trillion, surpassing the nation's defense budget. The current U.S. debt-to-GDP ratio stands at approximately 100%.

The timing of reaching the 210% threshold varies depending on economic growth. The Penn Wharton Budget Model estimated that the U.S. has 25 years before hitting this maximum in a lower-growth scenario. In a medium-growth scenario, the estimate is 22 years, while a higher-growth scenario shortens the timeline to 19 years. The model also indicated a 25% chance of reaching the debt maximum within 14 years, given the historical growth rate of healthcare costs.

The Treasury market currently holds over $30 trillion in outstanding securities and experiences more than $1 trillion in daily trading volume. U.S. Treasury bonds are traded in European markets. Historically, in 1790, the federal government consolidated debts from the Revolutionary War under a plan by then-Secretary of the Treasury Alexander Hamilton, assuming state debts and combining them into a national debt. The U.S. government committed to repaying these debts in full, and U.S. debt later helped finance the Louisiana Purchase.

The Congressional Budget Office projects the U.S. debt-to-GDP ratio to reach 175% by 2056.