use DateTime;

my $dt = DateTime->now(time_zone => 'UTC');
$dt->add( days => 13);    

print  substr( $dt->year, -2 ), 
       $dt->month < 10 ?  '0' :  '', 
       $dt->month;
[download]

Output:
0801

Update :

perl -MDateTime -e 'print
                    unpack( 
                           "x2A2xA2",
                           DateTime->now(time_zone => 'UTC')
                           ->add(days => 13)
                    );'
[download]

HTH,

PooLpi