sub _calculate_dates {
my $config = shift;
- my $cur_date = $config->start_date;
+ my $cur_date = $config->first_billing_date || $config->start_date;
my $start_date = $config->get_previous_invoice_date || DateTime->new(year => 1970, month => 1, day => 1);
my $end_date = $config->end_date || DateTime->new(year => 2100, month => 1, day => 1);
my $tomorrow = DateTime->today_local->add(days => 1);