I do my Go-Phone in 90 day/250 minute renewals.
I don't do a lot of calls, expecially since I live in a somewhat remote area and my home reception tends to vary from poor to none. Thus I always have plenty of minutes left over.
My minutes carry over, but if I renew before my expiration date, the new 90 days start on my renewal date and not on my previous expiration date. Thus, if I renew 10 days before expiration, I've just thrown away 10 days of subscription. A while back, I think I had an expiration because I thought I had more days than I did. Thus I lost my minutes (which is annoying in principle, if for no other reason).
I'm paying for 90 days and 250 minutes, not 90 minus something days and 250 minutes. The new 90 days should start at the previous expiration date, not the renewal date.
Minnemooseus