Best option long term is likely to get rid of this repeating field, replacing it with a table of related records, as it will likely be an ongoing problem for you.
I think this expression will work, but haven't tried using the extend function in years so I not have the syntax correct here:
Extend ( Today ) - day of Event
Then specify the number of repetitions for this calculation field that you have specified ofr Day of event.
Thanks for trying. Didn't work.
Your solution worked after I unchecked the "do not store calculation results" box.