How to renew without losing any days?

My Norton 360 will expire in 13 days. Can I renew today without losing these 13 days? I have an activation code for next year

The only way to not lose the time on your existing subscription is to contact Norton Support and ask them to add the time from the new product key to the existing subscription.    www.norton.com/contactcs

Or you can just wait until only one day left to enter the new key.