The WORKDAY(F5-1,1,...) step is a neat way to push a weekend or holiday due date forward, and the Dutta Mart row shows clearly why working days matter. Two things would trip it up in daily use. First, with the threshold at 3, an invoice reads "Remind now" on four working mornings in a row (3, 2, 1 and 0 days left), and the sheet cannot tell whether the nudge already went out on the first one. A "Reminded on" date in column K, tested in J5 before the Remind now check, for example IF(K5<>"","Reminded",...), turns the flag into a to-do that clears once it is done. Second, the holiday range. Six cells in L5:L10 is tight for a year of public and bank holidays, and the formulas only know the dates actually listed. An invoice raised in December on 30 or 45 day terms falls due in January, so next year's holidays need to be in the range before then. A taller range like L5:L40 costs nothing, since blank cells are ignored.