The Excel COUPDAYS function calculates the number of days in a coupon period that contains 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 shows the Excel Coupdays function, used to calculate the number of days in the period containing the settlement date, for a security that has the settlement date 01Jan2011, 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:
See the Microsoft Office website for further details and examples of the Excel Coupdays function.
If you get an error from the Excel Coupdays Function, this is likely to be one of the following:
#NUM!    Occurs if either:

#VALUE!    Occurs if either:
