use strict;
use warnings;
use DateTime;

my $dt1 = DateTime->new
(
    year  => 2013,
    month =>    9,
    day   =>   29,
);
 
my $dt2 = DateTime->new
(
    year  => 2013,
    month =>    3,
    day   =>   29,
);
 
my $dt3 = DateTime->new
(
    year  => 2013,
    month =>    3,
    day   =>   30,
);

my $dur1 = $dt2->subtract_datetime($dt1);
printf "29/03/2013 to 29/09/2013: %s months\n", $dur1->months;

my $dur2 = $dt3->subtract_datetime($dt1);
printf "30/03/2013 to 29/09/2013: %s months\n", $dur2->months;