Hi Esther, thanks for getting in touch!
Good question — yes, the license is annual and would need to be renewed each year. We do offer a discount on the renewal price, so there is relief. 🙂
One thing to note is that a license is not required to actually use the plugin. In other words, you can let the license expire and Events Calendar PRO will continue to function — you just won’t be able to access updates to the plugin or be able to post to the premium support forums on this site.
Does this help answer your question? Please let me know.
Cheers!
Geoff