My TV licence runs out soon. I always pay in full every year on the same day. I prefer to have it paid for that way. It costs slightly more to spread the cost out over the year.
The email reminder tells me to renew now. However they don't exactly explain how in doing so means it will expire in under 12 months next year.
If you're paying over the post office counter any decent staff member would advise you to wait until the start of the following month to qualify for the whole 12 months instead.