Can Word calculate how many days have passed since a given date?

Question

My Word document mentions one date, and I'd like to create a field that calculates how many days have passed since that date.

I know how to create a field that inserts today's date, and I know generally how to create a field that can calculate a formula, but it doesn't appear that Word will allow me to create a field that runs math on a date.

I know how to insert a bookmark to a cell in a table, but I can't get the table to run calculations based on dates.

And I know how to insert an Excel sheet where I can run formulas on dates, but I can't figure out how to draw a cell's contents into a line of text in the main Word file.

It seems like there has to be some way to do this, but I'm at a loss. Is there something I'm missing, or a reasonable workaround?