Don, if the constant is used in only one place, there is no real advantage to using a constant if its value is something obvious like "my constant". But you'll understand why it might be better to use DAYS_UNTIL_EXPIRY in code rather than GOMONTH(subsview.dsub_start,12*subsview.isub_duration)-DATE().
Also, the app may be subject to a standardized practice that sees all constant values #DEFINEd at the top of each proc, in which case you'd need to respect that standard.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
