How to automatically refresh a custom Contact field daily?

How to automatically refresh a custom Contact field daily?

Hi,
I created a field that calculates the days since a certain date from a Contact record. 
However, this field (see attachment) calculates that number of days only when that date is created. 
I would like that number to be calculated daily, since the number of days since that date should +1 every day.

How can I do that?
Thank you,