Windows console %DATE% Math

I posted the description below in some site some time ago:

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The following Batch files convert from Date to Julian Day Number an viceversa:

DATETOJULIAN.BAT:

@ECHO OFF
REM CONVERT DATE TO JULIAN DAY NUMBER
REM ANTONIO PEREZ AYALA
REM GET MONTH, DAY, YEAR VALUES
FOR /F "TOKENS=1-3 DELIMS=/" %%A IN ("%1") DO SET MM=%%A& SET DD=%%B& SET YY=%%C
REM ELIMINATE LEFT ZEROS
SET /A DD=10%DD% %% 100, MM=10%MM% %% 100
REM CALCULATE JULIAN DAY NUMBER
IF %MM% LSS 3 SET /A MM+=12, YY-=1
SET /A A=YY/100, B=A/4, C=2-A+B, E=36525*(YY+4716)/100, F=306*(MM+1)/10, JDN=C+DD+E+F-1524

JULIANTODATE.BAT:

REM CONVERT JULIAN DAY NUMBER TO MONTH, DAY, YEAR
REM ANTONIO PEREZ AYALA
SET /A W=(%1*100-186721625)/3652425, X=W/4, A=%1+1+W-X, B=A+1524, C=(B*100-12210)/36525, D=36525*C/100, E=(B-D)*10000/306001, F=306001*E/10000, DD=B-D-F, MM=E-1, YY=C-4716
IF %MM% GTR 12 SET /A MM-=12, YY+=1
REM INSERT LEFT ZEROS, IF NEEDED
IF %DD% LSS 10 SET DD=0%DD%
IF %MM% LSS 10 SET MM=0%MM%
REM SHOW THE DATE
ECHO %MM%/%DD%/%YY%

This way, to add/subtract a number of days to a date use the following lines:

CALL DATETOJULIAN %DATE%
SET /A NEWDATE=JDN+DAYS
CALL JULIANTODATE %NEWDATE%

Regards...

Reference: http://quasar.as.utexas.edu/BillInfo/JulianDatesG.html

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You just need to adjust your date format if it is not MM/DD/YYYY.