A Treasury bill, or T-bill, is a short-term government debt security with a maturity of less than one year. Unlike many other debt securities that make regular interest payments to investors, Treasury bills yield no interest. Rather, the bills are sold at a discount to their redemption price. For example, a Treasury bill with a face value of $1,000 might sell for $985.

Treasury bill prices are expressed on a scale where 100 represents full par value. So, the Treasury bill I just mentioned would have a price of 98.5.

Calculating the return of a Treasury bill

To calculate the return of a Treasury bill, we need to compare its par value to its face value. Additionally, since investment returns are most useful when expressed on an annualized basis, we'll also need to use the maturity period to convert the return to an annual percentage.

So the first thing you'll need to do is gather some information -- specifically, you'll need to know the Treasury bill's purchase price, date of purchase, and maturity date. From this information, you'll need to determine the number of days until maturity to be able to annualize the return.

The first calculation involves subtracting the T-bill's price from 100 and dividing this amount by the price. This figure tells you the T-bill's yield during the maturity period. Multiply this number by 100 to convert to a percentage.

Tbill

Next, multiply the yield you just calculated by 365 and then divide by the number of days in the maturity period that you determined earlier. This will give you the T-bill's annualized investment return.

Tbill

To illustrate, let's look at an example. Let's say you buy a 13-week Treasury bill (91 days to maturity) at a price of 99.0. During the maturity period, we can calculate the T-bill's yield as:

Tbill

Finally, to annualize the return, we can use our formula to calculate:

Tbill

This is the number you would use to compare your T-bill to other investment options. By annualizing the return, a 13-week T-bill's return can be easily compared with longer-dated T-bills as well as Treasury bonds, corporate bonds, and other types of fixed-income investments.

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