A to Z of Excel Functions: The COUPDAYBS Function

Welcome back to our regular A to Z of Excel Functions blog.  Today we look at the COUPDAYBS function.

The COUPDAYBS function

Bonds that pay interest prior to maturity are known as coupon bonds.  When you purchase such a bond, you should know how far into a coupon period you are buying the bond so you can tell how long you'll have to wait to receive your first interest payment.  You can calculate the number of days between the coupon beginning and settlement date using the coupon days between beginning settlement function, which is abbreviated to COUPDAYBS.  This function returns the number of days from the beginning of a coupon period until its settlement date.

The COUPDAYBS function employs the following syntax to operate:

The COUPDAYBS function has the following arguments:

• settlement: this represents the security's settlement date.  The security settlement date is the date after the issue date when the security is traded to the buyer
• maturity: this is the security's maturity date, i.e. when the security expires
• frequency: The number of coupon payments per year.  For annual payments, frequency is 1; for semiannual, frequency is 2; for quarterly, frequency is 4.  These are the only options (see below)
• basis: the type of day count basis to use.  This is optional.  There are five options:

It should be further noted that:

• Microsoft Excel stores dates as sequential serial numbers so they can be used in calculations. By default, January 1, 1900 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900
• dates should be entered using the DATE function, or as results of other formulae or functions.  For example, use =DATE(2020,2,29) for the 29^th of February, 2020.  Problems may occur if dates are entered as text
• the settlement date is the date a buyer purchases a coupon, such as a bond.  The maturity date is the date when a coupon expires.  For example, suppose a 30-year bond is issued on January 1, 2008, and is purchased by a buyer six months later.  The issue date would be January 1, 2008, the settlement date would be July 1, 2008, and the maturity date would be January 1, 2038, 30 years after the January 1, 2008, issue date
• all arguments are truncated to integers
• if settlement or maturity is not a valid date, COUPDAYBS returns the #VALUE! error value
• if frequency is any number other than 1, 2, or 4, COUPDAYBS returns the #NUM! error value
• if basis < 0 or if basis > 4, COUPDAYBS returns the #NUM! error value
• if settlement ≥ maturity, COUPDAYBS returns the #NUM! error value.

Please see my example below: 

We’ll continue our A to Z of Excel Functions soon. A full page of the function articles can be found here.