Business days: why subtracting two days per week is not enough
A date is not inherently a business day. Organisations can use different weekends and their own closures. A meaningful count starts with the working calendar you actually intend to use.
Define non-working days first
The model needs a date range, a weekly weekend pattern and a list of additional holidays. Microsoft’s NETWORKDAYS.INTL uses the same separation: a weekend is not a universal assumption.
ToolRoof checks both the starting and ending dates and counts either when it is a working day under your choices. A service that starts counting the following day may use a different convention.
References: Microsoft — NETWORKDAYS.INTL
A closure is deducted only once
A holiday already falling on a weekend does not remove another day. Repeating a holiday date does not create two holidays, and a date outside the period does not change the answer.
Use the organisation’s actual calendar. The calculator does not automatically know every national, local or exceptional holiday, and an incomplete input list is not an official calendar.
A count is not a delivery commitment
Working days between two dates help estimate attendance or scheduling capacity. They do not establish how long a particular task takes. Order cut-off times, partial closures and half-days require additional rules.
Before comparing two delivery promises, check when counting begins, the provider’s weekend and included holidays. Two promises of “5 days” need not imply the same arrival date.
Worked example: two weeks and one additional holiday
The inclusive period 2026-09-01 to 2026-09-14 contains 14 calendar dates. Assuming Saturday and Sunday are non-working, 4 are weekends and 10 are working days. This is an illustrative calendar, not a statement of any country’s weekend.
Adding a holiday on 2026-09-07 leaves 9 working days. Also listing 2026-09-06, a Sunday in this example, does not reduce the answer to 8: that date was already excluded.