To add or subtract days from any date, copy the script below or download here and save as DateMath.cmd
@Echo off SETLOCAL :: DateMath, a general purpose date math routine :: If DateMath detects an error, variable _dd_int is set to 999999. SET v_dd_int=0 SET v_mm_int=0 SET v_yy_int=0 SET v_ymd_str= SET v_mm_str= SET v_dd_str= IF "%3"=="" goto s_syntax IF "%4"=="+" goto s_validate_year IF "%4"=="-" goto s_validate_year IF "%4"=="" goto s_validate_year :s_syntax echo: echo DATEMATH SYNTAX: echo _______________ echo: echo DateMath will set the variables as listed below echo 'str' variables include leading zeros e.g. "01" echo 'int' variables leading zeros are stripped e.g. "1" echo: echo CALL DateMath YYYY MM DD - YYYY2 MM2 DD2 echo: echo Will set variable _dd_int to the signed difference echo between the 2 dates (measured in days) echo: echo: echo CALL DateMath YYYY MM DD +/- Days echo: echo Will set the following variables to the result of echo adding or substracting days from the initial date: echo _ymd_str, _yy_int echo _mm_str, _mm_int, echo _dd_str, _dd_int echo: echo _yy_int is in YYYY format, even if YY format was originally supplied. echo: ENDLOCAL & SET /a _dd_int=999999 goto :eof :s_validate_year ::strip leading zeros SET v_yy=%1 if %v_yy:~0,1% EQU 0 set v_yy=%v_yy:~1% :: Check for Y2K IF %v_yy% LSS 100 IF %v_yy% GEQ 80 SET /A v_yy += 1900 IF %v_yy% LSS 80 SET /A v_yy += 2000 :: at this point v_yy contains a 4 digit year ::validate month and day if %2 GTR 12 goto s_syntax if %3 GTR 31 goto s_syntax SET v_mm=%2 SET v_dd=%3 ::strip leading zeros if %v_mm:~0,1% EQU 0 set v_mm=%v_mm:~1% if %v_dd:~0,1% EQU 0 set v_dd=%v_dd:~1% :: Set the int variables SET /a v_dd_int=%v_dd% SET /a v_yy_int=%v_yy% SET /a v_mm_int=%v_mm% :: Determine which function to perform - ADD, SUBTRACT or CONVERT If not "%6"=="" goto s_validate_2nd_date if "%4"=="" goto s_convert_only :: Add or subtract days to a date SET /a v_number_of_days=%5 goto s_add_or_subtract_days :s_convert_only SET /a v_dd_int=%v_dd% IF %v_dd% LEQ 9 (SET v_dd_str=0%v_dd%) ELSE (SET v_dd_str=%v_dd%) IF %v_mm% LEQ 9 (SET v_mm_str=0%v_mm%) ELSE (SET v_mm_str=%v_mm%) SET v_ymd_str=%v_yy%%v_mm_str%%v_dd_str% ECHO DATEMATH - Convert date only (no maths) goto s_end :::::::::::::::::::::::::::::::::::::::::::::::::: :s_validate_2nd_date If "%4"=="+" goto s_syntax :: Subtracting one date from another :::::: :: strip leading zero SET v_yy2=%5 if %v_yy2:~0,1% EQU 0 set v_yy2=%v_yy2:~1% if %v_yy2% GTR 99 goto s_validate2nd_month if %v_yy2% GTR 49 goto s_prefix_2_1950_1999 if %v_yy2% LSS 10 goto s_prefix_2_2000_2009 SET v_yy2=20%v_yy2% goto s_validate2nd_month :s_prefix_2_2000_2009 SET v_yy2=200%v_yy2% goto s_validate2nd_month :s_prefix_2_1950_1999 SET v_yy2=19%v_yy2% :s_validate2nd_month ::strip leading zeros ::SET /a v_yy2=%v_yy2% if %v_yy2:~0,1% EQU 0 set v_yy2=%v_yy2:~1% ::v_yy2 now contains a 4 digit year if %6 GTR 12 goto s_syntax SET v_mm2=%6 if %7 GTR 31 goto s_syntax SET v_dd2=%7 ::strip leading zeros ::SET /a v_mm2=%v_mm2% if %v_mm2:~0,1% EQU 0 set v_mm2=%v_mm2:~1% ::SET /a v_dd2=%v_dd2% if %v_dd2:~0,1% EQU 0 set v_dd2=%v_dd2:~1% call :s_julian_day %v_yy_int% %v_mm_int% %v_dd_int% SET v_sumdays1=%v_JulianDay% call :s_julian_day %v_yy2% %v_mm2% %v_dd2% SET v_sumdays2=%v_JulianDay% SET /a v_dd_int=%v_sumdays1% - %v_sumdays2% ECHO DATEMATH - Subtracting one date from another = days difference ECHO ~~~~~~ ECHO %v_dd_int% ECHO ~~~~~~ goto s_end_days :::::::::::::::::::::::::::::::::::::::::::::::::: :s_add_or_subtract_days if /i "%4"=="+" goto s_add_up_days :: Subtract all days :::::: SET /a v_dd=%v_dd% - %v_number_of_days% :s_adjust_month_year if %v_dd% GEQ 1 goto s_add_subtract_days_DONE SET /a v_mm=%v_mm% - 1 if %v_mm% GEQ 1 goto s_add_days_%v_mm% SET /a v_yy=%v_yy% - 1 SET /a v_mm=%v_mm% + 12 goto s_add_days_%v_mm% :s_add_days_2 SET /a v_dd=%v_dd% + 28 SET /a v_leapyear=%v_yy% / 4 SET /a v_leapyear=%v_leapyear% * 4 if %v_leapyear% NEQ %v_yy% goto s_adjust_month_year SET /a v_dd=%v_dd% + 1 goto s_adjust_month_year :s_add_days_4 :s_add_days_6 :s_add_days_9 :s_add_days_11 SET /a v_dd=%v_dd% + 30 goto s_adjust_month_year :s_add_days_1 :s_add_days_3 :s_add_days_5 :s_add_days_7 :s_add_days_8 :s_add_days_10 :s_add_days_12 SET /a v_dd=%v_dd% + 31 goto s_adjust_month_year :s_add_up_days :: add all days :::::: SET /a v_dd=%v_dd% + %v_number_of_days% :s_subtract_days_ goto s_subtract_days_%v_mm% :s_adjust_mth_yr SET /a v_mm=%v_mm% + 1 if %v_mm% LEQ 12 goto s_subtract_days_%v_mm% SET /a v_yy=%v_yy% + 1 SET /a v_mm=%v_mm% - 12 goto s_subtract_days_%v_mm% :s_subtract_days_2 SET /a v_leapyear=%v_yy% / 4 SET /a v_leapyear=%v_leapyear% * 4 If %v_leapyear% EQU %v_yy% goto s_subtract_leapyear if %v_dd% LEQ 28 goto s_add_subtract_days_DONE SET /a v_dd=%v_dd% - 28 goto s_adjust_mth_yr :s_subtract_leapyear if %v_dd% LEQ 29 goto s_add_subtract_days_DONE SET /a v_dd=%v_dd% - 29 goto s_adjust_mth_yr :s_subtract_days_4 :s_subtract_days_6 :s_subtract_days_9 :s_subtract_days_11 if %v_dd% LEQ 30 goto s_add_subtract_days_DONE SET /a v_dd=%v_dd% - 30 goto s_adjust_mth_yr :s_subtract_days_1 :s_subtract_days_3 :s_subtract_days_5 :s_subtract_days_7 :s_subtract_days_8 :s_subtract_days_10 :s_subtract_days_12 if %v_dd% LEQ 31 goto s_add_subtract_days_DONE SET /a v_dd=%v_dd% - 31 goto s_adjust_mth_yr :s_add_subtract_days_DONE SET /a v_dd_int=%v_dd% SET /a v_mm_int=%v_mm% SET /a v_yy_int=%v_yy% IF %v_dd% GTR 9 (SET v_dd_str=%v_dd%) ELSE (SET v_dd_str=0%v_dd%) IF %v_mm% GTR 9 (SET v_mm_str=%v_mm%) ELSE (SET v_mm_str=0%v_mm%) SET v_ymd_str=%v_yy%%v_mm_str%%v_dd_str% ECHO DATEMATH - add or subtract days from a date = new date goto s_end :::::::::::::::::::::::::::::::::::::::::::::::::: :s_julian_day SET v_year=%1 SET v_month=%2 SET v_day=%3 SET /a v_month=v_month SET /a v_day=v_day SET /A a = 14 - v_month SET /A a /= 12 SET /A y = v_year + 4800 - a SET /A m = v_month + 12 * a - 3 SET /A m = 153 * m + 2 SET /A m /= 5 SET /A v_JulianDay = v_day + m + 365 * y + y / 4 - y / 100 + y / 400 - 32045 ECHO The Julian Day is [%v_JulianDay%] goto :eof :::::::::::::::::::::::::::::::::::::::::::::::::: :s_end ECHO ~~~~~~~~~~~~ ECHO [%v_ymd_str%] YY=[%v_yy_int%] MM=[%v_mm_str%] DD=[%v_dd_str%] ECHO ~~~~~~~~~~~~ :s_end_days ENDLOCAL&SET /a _yy_int=%v_yy_int%&SET /a _mm_int=%v_mm_int%&SET /a _dd_int=%v_dd_int%&SET _ymd_str=%v_ymd_str%&SET _mm_str=%v_mm_str%&SET _dd_str=%v_dd_str%
In other languages, performing basic math on date values is much easier, PowerShell has .addDays, VBScript has DateAdd, both of which accept negative numbers for subtractions.
D:\> datemath 2021 05 08
DATEMATH - Convert date only (no maths)
~~~~~~~~~~~~
[20210508] YY=[2021] MM=[05] DD=[08]
~~~~~~~~~~~~
D:\> datemath 2027 12 01 - 2002 11 02
The Julian Day is [2461741]
The Julian Day is [2452581]
DATEMATH - Subtracting one date from another = days difference
~~~~~~
9160
~~~~~~
D:\> datemath 2002 11 02 + 9160
DATEMATH - add or subtract days from a date = new date
~~~~~~~~~~~~
[20271201] YY=[2027] MM=[12] DD=[01]
~~~~~~~~~~~~
D:\> datemath 2012 09 08 - 2011 09 08
The Julian Day is [2456179]
The Julian Day is [2455813]
DATEMATH - Subtracting one date from another = days difference
~~~~~~
366
~~~~~~
"We were having one of those great first dates you can only have when it’s not an actual date" ~ Sarah Jessica Parker
tdiff.cmd - Calculate the difference in Hours/Mins between two time values.
SetLocal - Control the visibility of environment variables in a batch file.
How-to: PowerShell variables - these support Math operations out of the box (.addDays)
Rules for how CMD.EXE parses numbers - DosTips forum (Dave Benham).