The Excel TBILLEQ function returns the bond-equivalent yield for a Treasury bill, based on a settlement date, a maturity date, and a discount rate. In the example shown, the settlement date is 5-Feb-2019, the maturity date is 1-Feb-2020, and the discount rate is 2.54%. The formula in F5 is:
In Excel, dates are serial numbers. Generally, the best way to enter valid dates is to use cell references, as shown in the example. To enter valid dates directly inside a function, the DATE function is the best option.
About treasury bills
A treasury bill (also called a T-Bill) is a short-term debt obligation issued by the US Treasury Department. T-Bills are sold in increments of $100, and have terms that range from a few days up to 52 weeks. Backed by US government, T-Bills are considered a low risk investment.
T-Bills are typically sold at a discount from par amount (face value), and the discount rate is determined at auction. However, T-bills can also be sold at a premium, when the price is greater than the par amount.
T-Bills do not offer regular interest payments like a coupon bond. However, when a T-Bill matures, the owner is paid it's par amount, or face value. When the par value is greater than the purchase price, the difference is the interest earned.