Don't expect people to keep track of their subscriptions.
For MICROCAR NEWS magazine I have this printed on their label:
Last Issue is: #4 2012
above their name.
If that issue is actually their last issue it says this:
Last Issue is: THIS ONE! Renew Now!
For people that pay attention, that gets some.
I have to do a mass email reminder for the next group, that catches maybe 1/3 of the remaining. And of course it only includes people who have opted to provide an email address.
The remainders get a letter reminder in the mail with a return envelope. That covers another 1/3, the rest just fade off.
Oddly enough while the letter reminder is more labor-intensive, it is less costly per renewal if they send in a check because no PayPal fees.
And then there are just people that don't respond to anything and they end up renewing very late, maybe 6 months later.
Lots of people subscribe to many many publications and they are constantly reminded year-round to renew by all of them.