Your new SSL Certificate will be connected with the old one, which means that all the remaining days from the previous SSL Certificate will be added to the new one.
If you have a Domain Validation SSL Certificate, you can renew your SSL Certificate 1-2 weeks prior to your SSL Certificate’s expiration date.
Your SSL Certificate expires on its “Expires” date. Also, you should plan to have the SSL Certificate renewed enough time ahead so that you manage to install it on your website and server before your current SSL Certificate expires.
If you have a Business Validation SSL Certificate or an Extended Validation SSL Certificate, then we recommend renewing your SSL Certificate 3-4 weeks prior to the expiration date, so as you have to pass the Business Validation or Extended Validation again.
The Business Validation or Extended Validation process is quicker when renewing an SSL Certificate than when getting it for the first time.
Anyway, it is always good to do this as early as possible, in order to assure the continuity of your website being secured by an SSL Certificate.