Here is one way using Date::Calc, but there are a lot of other modules you could use as well. This assumes that the epoch is 0/0/1900 as opposed to 1/1/1900 but either way it is easy to change.

    #!/usr/bin/perl -wl

    use strict;
    use Date::Calc 'Delta_Days';


    print days_since_1900(1900, 1, 1);
    print days_since_1900(2006, 5, 13);


    sub days_since_1900 {

        my $years   = $_[0];
        my $months  = $_[1] || 1;
        my $days    = $_[2] || 1;

        my @date    = ($years, $months, $days);
        my @epoch   = (1900,   1,       1,   );

        my ($days_since_1900) = Delta_Days(@epoch, @date);

        return 1 + $days_since_1900;
    }
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--
John.