If your site footer is built using a content category and therefore can be edited using the full editor rather than in the Site Preferences you can use a built-in macro to include the year in your footer. This can be useful for copyright statements.
For example if you want to state that the site content is copyright by your company (Acme Inc.) from 2011 until now you could enter the following in the editor:
© 2011-[[Calc;year]] Acme Inc.
which would then be rendered:
© 2011-2023 Acme Inc.