+=item balance_date TIME
+
+Returns the balance for this customer, only considering invoices with date
+earlier than TIME (total_owed_date minus total_credited minus
+total_unapplied_payments). TIME is specified as a UNIX timestamp; see
+L<perlfunc/"time">). Also see L<Time::Local> and L<Date::Parse> for conversion
+functions.
+
+=cut
+
+sub balance_date {
+ my $self = shift;
+ my $time = shift;
+ sprintf( "%.2f",
+ $self->total_owed_date($time)
+ - $self->total_credited
+ - $self->total_unapplied_payments
+ );
+}
+