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).