Thanks. This is helpful. I'll try your refinements.

Although I didn't ask about it the first time around, I'm still
confused about what the volatile line is supposed to do when it's true
vs. when it's false. (The Help file is kind of cryptic.)

On my sheet, I've tried it both ways. True seems better. I'd prefer
the function (deadline dates) to recalculate when I alter the dates in
the HolidayList, and true causes that to happen. (It doesn't matter
that much, because the worksheet is intended to provide a quick
calculation of ad hoc deadline dates for the user; the data cells will
clear upon close.)

Sometimes, whether volatile is set to true or false, a #Value! error
appears in the result (deadline) cell, and F9 doesn't resolve it. I
have to enter fresh (or the same) data manually to force a
recalculation.

Thanks again.