Triggers

I'm using this funtion via a trigger to total up amounts in several fields
(and adding that value into a total field)..

CREATE FUNCTION invoice_total_trigger() RETURNS OPAQUE AS '
BEGIN
NEW.total := NEW.fee_membership + NEW.fee_logins + NEW.fee_convention +
NEW.fee_prints+ NEW.fee_hotlines + NEW.fee_postage + NEW.fee_ups +
NEW.fee_late + NEW.fee_other1 + NEW.fee_other2 + NEW.fee_other3 +
NEW.fee_pastdue;
RETURN NEW;
END;
' LANGUAGE 'plpgsql';

That's the function, here is the trigger.

CREATE TRIGGER invoice_total_trigger AFTER INSERT OR UPDATE ON invoice
FOR EACH ROW EXECUTE PROCEDURE invoice_total_trigger();

It works for updating but not when you insert a new row. Am I doing it
wrong?

I need the invoice_total_trigger to run every time a row is updated or
inserted..

Thanks guys!

-Mitch