use DateTime;
use Data::Dumper;

my $date = DateTime->now;

my $dur = $date->subtract_datetime( DateTime->now->subtract( years => 1, months => 1 ) );
print "\nmonths: " . $dur->in_units( 'months' ) . "\ndays: " . $dur->in_units( 'days' ) . "\n";

__OUTPUT__
months: 13
days: 0
^^^^^^^