Why "business days between two dates" isn't a division problem (I only saw it clearly building a workday calculator)

Business-day counting cannot be solved by simply dividing total days by seven.

Full 7-day blocks can be counted directly, but leftover days must be checked against a custom workday set.

Partial weeks depend on which weekdays fall in the range, so custom work schedules must be handled explicitly.

The same full-week-plus-remainder logic also works in reverse when adding workdays to a date.

Accurate deadline and scheduling tools need to account for weekday patterns and date direction to avoid errors.