Why both the start and end date count#
If work starts on a Monday and finishes that same Friday, that is five business days, not four — the count is inclusive of both endpoints, matching how a working week is actually described. A calculator that treats the range as exclusive would undercount by one whenever both ends land on a business day, which is the more common case.
Why holidays are something you list, not something this tool assumes#
Public holidays differ by country, and often by region or industry within a country — a calculator that bakes in one country's calendar gives a subtly wrong answer to everyone outside it, without any indication that it did. This tool leaves the holiday list entirely up to you: paste the specific dates that matter for your situation, one per line, and only those get excluded. It costs a small amount of manual entry in exchange for never silently assuming the wrong country's calendar.
What counts as a "business day" here#
A business day is any Monday through Friday that is not on your holiday list — Saturday and Sunday are always excluded automatically, since that is the one part of the definition that does not vary by region. If your organization uses a different weekend (some countries treat Friday-Saturday as the weekend instead), that distinction is not currently configurable here, since it changes the core weekend assumption rather than just adding exceptions.