Daily treasury bill rates can be accessed at the U.S. Treasury Department website. The Treasury Department states that the Federal Reserve bank of New York acquires market quotations at or about 3:30pm every business day. The four-week, 13-week, 26-week and 52-week secondary market quotations are provided.
Each of the four periods on the daily treasury bill rates chart offer both the bank discount rate and the coupon equivalent. In addition to the daily quote the rates can be viewed for either the year to date or previous years. Additionally you can view charts showing other interest rate data including yield curves, long term rates, real long term rates and historical rates, states the U.S. Department of the Treasury.