Date and time calculations are tough to get right, especially the nitty-gritty like leap years and daylight savings times. That's why there's a bunch of modules on CPAN, dealing with these problems: Check out DateTime, or for simpler calculations, use Date::Calc and Date::Manip. Example:

    use DateTime;

    my $dt1 = DateTime->new(
        year   => 2005,
        month  => 10,
        day    => 31,
        hour   => 0,
        minute => 0,
        second => 01,
    );

    my $dt2 = DateTime->new(
        year   => 2005,
        month  => 11,
        day    => 01,
        hour   => 0,
        minute => 0,
        second => 01,
    );

    my $duration = $dt2 - $dt1;
    print $duration->in_units('days'), "\n";
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