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The day-count convention (DCC) determines how the day-count fraction (DCF) is found when calculating accrued interest. The day-count convention on your bond is defined in the accompanying indenture (contract).  For example, 30 days in a month and 360 days in a year would mean a DCC of 30/360. Other bonds, especially U.S. government (Treasury) bonds,  calculate interest using the exact number of days in a month and year. Such a DCC is  sometimes referred to as "actual/actual" or "ACT/ACT."  In practice, bonds can also use a combination of these two DCCs, with such possible DCCs as 30/ACT and ACT/360. In practical terms, the convention used will make very little difference in terms of interest earned. Double-check your bond indenture to be sure. Your interest rate, also called the the coupon rate, specifies the amount of interest you earn on the bond annually as a percentage of your par (or "face") value. The payment frequency signifies whether your bond pays interest once a year or more often. Bonds typically pay interest either annually or semi-annually (once or twice per year).  This information can be found within your bond indenture. For example, your bond might pay a 6% coupon rate twice per year. In this case, the annual interest rate would be 6% divided by the number of payments within the year. Thus, a 6% bond that pays interest twice per year would effectively pay 3% of the par value for each of the two payments during the year, or 6% total. Search your records to see when your bond made its latest coupon payment. This information is available from the financial institution that sold you the bond. This will depend on your DCC, as the passage of days is calculated differently in each type of bond. Generally, if your bond is actual/actual, you will actually count the days. If your bond is 30/360, you would use those numbers for each month or year that has passed.   Let's say you have a 30/360 bond, and exactly two months have passed since your latest payment. You would simply multiply 2 x 30 and use 60 days in your calculations, regardless of how many days there actually were in the elapsed months. This is the amount paid to the holder of the bond at maturity (when the interest payments stop).  This will be stated clearly on your bond indenture.  Note that the par value may be more or less than what you actually paid for the bond originally. Market price is affected by the existing rate environment and the bond issuer's creditworthiness.   Bonds are often valued at $1000. That would be the par value even if you paid slightly more or less for it.
Determine the day-count convention on your bond. Confirm the interest rate and payment frequency on your bond. Find when the most recent coupon payment was made. Calculate how many days have passed since the most recent coupon-paying day. Confirm the face or par value of your bond.