The U.S. Treasury publishes daily interest rate data on its website at home.treasury.gov. The data shows how much interest the government pays to borrow money for different lengths of time, from a few months to 30 years. Bond traders, risk managers, and economists rely on this information to track the government's borrowing costs.

For historical data, Treasury maintains an archives page at home.treasury.gov. Users can choose from three data types: Daily Treasury Par Yield Curve Rates, Daily Treasury Bill Rates, and Daily Treasury Long-Term Rates. The Long-Term Rates series is built as an average rather than a direct yield. That difference matters when the data is used to compare other investments or to calculate the present value of future money.

Treasury also publishes a separate "Daily Treasury Real Long-Term Rates" series, which is different from the nominal (not adjusted for inflation) Long-Term Rates (home.treasury.gov; Treasury press release). The real rates series factors in expected inflation by comparing regular Treasury bonds to Treasury Inflation-Protected Securities (TIPS), which adjust their payouts for rising prices. Mixing the two without noting how each is calculated is a common error.

The Treasury Yield Curve Methodology page, last published February 18, 2025, at home.treasury.gov, explains the technical approach Treasury uses to build its yield curve from market data. For anyone building or checking models against Treasury's numbers, this page explains how the department fills in gaps between data points, smooths the curve, and chooses which securities to include.

One gap in the data deserves particular attention. Treasury stopped publishing the 30-year rate on February 18, 2002, and did not resume it until February 9, 2006 (home.treasury.gov; FRED; Federal Reserve H.15). That gap means any analysis covering the early 2000s will hit a hole at the 30-year mark. Models using data from that period need to account for the missing 30-year rate, either by estimating it from nearby maturities or by flagging that period as incomplete.

The Treasury Constant Maturity Rates dataset, also available through the Office of Financial Research, provides a daily view of the yield curve's shape across all maturities. For those watching for curve inversions — when short-term rates exceed long-term rates, a widely watched recession signal — this construction allows consistent comparisons across dates, even as the underlying securities change over time.

The broader context here is that these datasets are not just reference tables. They serve as the foundation for valuing everything from mortgage-backed securities to corporate bonds, and they feed directly into the Fed's H.15 statistical release that underpins countless financial contracts and regulatory capital calculations. The distinction between par yields, averages, and real rates is not academic. A model that uses the Long-Term Rates averages when it should be using par yields from the curve will systematically misprice sensitivity to interest-rate changes at the long end.

The 30-year gap from 2002 to 2006 is the kind of break that can silently corrupt a backtest. Anyone running multi-decade analysis on bond risk premiums or the slope of the curve should verify that their data provider handled the gap explicitly rather than papering over it. The series now has roughly two decades of uninterrupted data since February 2006, but that four-year hole remains a live issue for long-term work.

One practical point for anyone pulling this data through software: the distinction between the par yield curve rates and the long-term average rates is not always clearly labeled by third-party providers. Treasury's own pages keep them separate, but Bloomberg, FRED, and other aggregators may use names that hide which method was used. Checking the series against Treasury's published methodology page eliminates that ambiguity.