@SkrOYC Thanks my friend 
I’m sorry this is taken from a French app and I thought changing the display names to English would be enough to make it understandable. I will change the column names and formulas accordingly. Thank you. Update: sorry this has proven to be too time consuming. Please tell me should you have difficulties and I’ll be happy to assist; there’s basically only one formula in the app.
Regarding the dates table, due to lack of iteration expressions in AppSheet, I had to make a choice between:
-
generating the dates list on the fly using either:
- recurrent behavior actions,
- calling js libraries from the sheet.
AppSheet’s WORKDAY() is probably using a C* library for such on-the-fly generation of dates, and this library itself possibly contains a static list of dates, topping at year 9999.
-
or just having a static date list ready, in a table.
I opted for the latter because it makes calculations immediate and is just simpler.
And you are right, this calculator is a solution for the inability to define arbitrary week workdays in WORKDAY().