$40 Trillion and Shrinking. For Now.

The US national debt dipped slightly this week, falling from $40.074 trillion to $40.048 trillion between September 9 and September 10. A $26 billion daily drop sounds significant until you remember that daily debt figures swing constantly based on Treasury cash flows, tax receipts, and spending timing. The more important number is the one hiding in plain sight: debt is up nearly 5% over the past year, adding roughly $1.9 trillion since this time in 2025.

That 5% annual growth rate matters in a specific way right now. Interest rates are sitting in the upper quarter of their historical range, which means the government is refinancing old, cheap debt into new, expensive debt every time a Treasury bill or note matures. The Congressional Budget Office has flagged net interest payments as one of the fastest-growing line items in the federal budget, a dynamic that compounds when both the debt stock and the rate applied to it are rising simultaneously.

Historically, when debt grows faster than the economy’s nominal output, the debt-to-GDP ratio climbs. That ratio is the one bond investors and credit markets watch most closely, because it measures the government’s capacity to service what it owes. In past cycles, a rising debt-to-GDP ratio alongside high long-term rates has pushed investors to demand incrementally higher yields as compensation, which feeds back into borrowing costs for everyone, including businesses financing growth.

For anyone thinking about capital allocation or long-term financing, the question this raises is straightforward: if the cost of government borrowing stays elevated, how does that interact with corporate borrowing costs and investment decisions over the next few years?

Bottom Line: The daily wiggle in the debt figure is noise. The underlying trend of nearly $2 trillion in new debt per year, financed at historically high rates, is the signal worth watching.

Source: US Treasury Fiscal Data

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