You must pay your renewal fees by the current expiration date of your domain name.  Your domain registrar will notify you 30 days before your name is due to expire.

However, you do not need to wait until the expiration date.  You can renew your domain name at any time and for any number of years up to a total of ten.  With a 10 year renewal, you won't have to worry about your domain name expiring for a long long time.