When you renew your account, no matter whether you renew it exactly on its expiration date or a few days/weeks/months prior, the renewal will count from the account's expiration date.
For example, if your account expires on the 9th of January 2018 and you renew it for one year on the 2nd of January 2018, then the new expiration date will be the 9th of January 2019, not the 2nd of January 2019.