I have scripted DaysMonth.bat to return the number of days in the month for a specified date.

The syntax for using DaysMonth.bat is:

\[call\] DaysMonth Date Days

Where:

Date contains a valid date.                              Days is a call directed numeric environment variable that will contain the                               number of days in the month for Date.
DaysMonth.bat contains:
                              @echo off                              if \{%2\}==\{\} @echo DaysMonth Date Days&goto :EOF                              if exist "%TEMP%\DaysMonth.vbs" goto doit                              @echo.Dim Arguments>"%TEMP%\DaysMonth.vbs"                              @echo.Set Arguments = Wscript.Arguments>>"%TEMP%\DaysMonth.vbs"                              @echo.yyyy = DatePart("yyyy", Arguments(0))>>"%TEMP%\DaysMonth.vbs"                              @echo.mm = Right(100+DatePart("m", Arguments(0)),2)>>"%TEMP%\DaysMonth.vbs"                              @echo.ld = Day(DateSerial(yyyy, 1 + mm, 0))>>"%TEMP%\DaysMonth.vbs"                              @echo.wScript.Echo ld>>"%TEMP%\DaysMonth.vbs"                              :doit                              set /a %2=0                              for /f "Tokens=*" %%a in ('cscript //nologo "%TEMP%\DaysMonth.vbs" %1') do (                               set /a %2=%%a                              )