Source: US Treasury Monthly Statement of the Public Debt and Average Interest Rates on US Treasury Securities, Monetary Macro. As of 2026-10-31. Released 2026-11-12.

Marketable Treasury debt at each month-end from January 2001, from the Monthly Statement of the Public Debt (per-security amounts, inflation-adjusted) and Treasury's official monthly average interest rates by security type. Months appear when both are published, about two weeks after month-end.

Annualized interest expense = for each of bills, notes, bonds, TIPS, floating rate notes and the Federal Financing Bank, the amount outstanding times its average interest rate, summed. It is what the debt outstanding costs per year at the rates then on it: cash coupons and bill discount. It is not the interest the government paid in the year, and it leaves out the inflation compensation on TIPS.

The all-marketable average rate is Treasury's published Total Marketable rate, which leaves TIPS out of its weighting (a TIPS coupon is a real rate on inflation-adjusted principal). It is reproduced from the debt statement every month as a check, within 0.1 percentage point. Bills are valued at face (maturity) value.

Weighted average maturity is the remaining time to maturity of each security weighted by its amount outstanding, in years, shown with and without bills. It reads about 70 months in 2026, close to the 71 months reported elsewhere.