Convert a date field to a date and time field

I need to show users how many days something is overdue.

The due date is in a date only field.

All the date difference functions usable in calculated fields require the two dates being compared to have the same format (date only or date and time).

There is a NOW() function that give date and time, but there doesn't seem to be a Today() function that would give me today's date-only date.

Do I need to rip out my old fields and replace them with date/time fields?

Or is there another approach?

I'm sure this would be easy in JavaScript, but that's beyond me.

Thanks for any ideas.

Jessica Weissman