The Excel Coupdaybs function calculates the number of days from the beginning of a coupon's period to the settlement date.
The syntax of the function is:
Where the arguments are as follows:
settlement    The settlement date of the security.  
maturity    The maturity date of the security.  
frequency   
An integer, representing the number of coupon payments per year. This must have the value 1, 2, or 4, meaning:


[basis]   
An optional integer argument that specifies the day count basis to be used. This must be one of the following values:

Note that the settlement and maturity dates should be input as either:
Warning: If you attempt to input these dates as text, there is a chance that Excel may misinterpret them due to different date systems, or date interpretation settings on your computer.
Cell A3 of the spreadsheet below contains an example of the Excel Coupdaybs function, used to calculate the number of days from the beginning of a coupon's period to the settlement date. The security has the settlement date 01Jan2011, the maturity date 25Oct2012, and 4 payments per year. The US (NASD) 30/360 day count basis is used.
Formulas:

Results:

Note that, in the above example:
For further details and examples of the Excel Coupdaybs function, see the Microsoft Office website.
If you get an error from the Excel Coupdaybs Function, this is likely to be one of the following:
#NUM!   
Occurs if either:

#VALUE!   
Occurs if either:
