Treasury Long-Term Average Rate and Extrapolation Factors. Beginning February 18, 2002, Treasury ceased publication of the 30-year constant maturity series. Instead, from February 19, 2002 through May 28, 2004, Treasury published a Long-Term Average Rate, "LT>25," (not to be confused with the Long-Term Composite Rate, definitions below). In addition, Treasury published daily linear extrapolation factors that could be added to the Long-Term Average Rate to allow interested parties to compute an estimated 30-year rate. On June 1, 2004, Treasury discontinued the "LT>25" average due to a dearth of eligible bonds. In place of the "LT>25" average, Treasury published the Treasury 20-year Constant Maturity rate on this page along with an extrapolation factor that was added to the 20-year Constant Maturity to obtain an estimate for a theoretical 30-year rate.