Yes, when you place an order for an SSL Certificate the system will check to see if you already have an SSL Certificate issued by the Certificate Authority. It will then get the remaining months and add those months onto your new order. This is generally how you renew your certificate as SSL Certificates can not have their expiry date extended due to the date being hard coded into them. To obtain remaining months on your new order/renewal it will need to be the exact same domain name and SSL Certificate type from the same Certificate Authority.
We do have an auto renewal system that will automatically place a new renewal order for you close to the expiry date on payment of the renewal invoice.