expiry date

I'm waiting for an update for the expiry date. It should be a forwards calculation for the date expiry and never reverse. My passwords expire after 30 days, 60 days, 90 days or 180 days. It moves forwards and never back in time. I would change the password today and set expiry to remind me 1 day before or 1 week before. This never happens. I really don't yet understand the reason for such a setup. I would really want to know the login behind this situation.