Number of Days Between Dates

My other field is a numeric field that tracks the number of events that occur each day. These events don't occur everyday. How can I count back to the most recent day that one of these events occurred?

You will need to get that "most recent day" as a field on the record so that it is available to use in a formula.  If these Events are in a child table, you will need to edit the relationship to create a Summary field of the maximum Event Date.

I'm not quite understanding how to get the most recent day into the equation. I have a date field, but the only one that matters is the most recent.

Do you have a date field on the same record as where you need the formula or is that date field in a child table?  Do you have relationships?  Or do you simply have a bunch of date fields on the record itself and you want the most recent to be used.