Business Days Between Dates Calculator

The business days between dates calculator counts the Monday-through-Friday working days in any date span, then removes the holiday dates you add. It also reports calendar days, weekend days, and full weeks so you can see how the working-day count relates to the raw length of the span.

Use it for project deadlines, delivery promises, notice periods, invoice due dates, onboarding timelines, or any plan where “three business days” or “two weeks of work” needs a concrete calendar answer.

What this calculator does

You enter a start date and an end date, and optionally a list of holiday dates such as public holidays, company shutdown days, or personal days off. The primary result is the number of business days in the span — every weekday that is not one of your holidays. Supporting results show:

• Calendar days — every day in the span, including weekends and holidays, with both endpoints counted.
• Weekends — the Saturday and Sunday days inside the span.
• Full weeks — how many complete 7-day blocks the span contains, with the leftover days noted.
• Holidays excluded — how many of your holiday entries actually reduced the count.

The count treats the start date and end date as inclusive. If you need a span that excludes one endpoint (for example, “days from today, not counting today”), add one day to the later date or adjust by hand.

How the counting works

The calculation uses the calendar-week convention from ISO 8601, in which weeks run Monday through Sunday. Under that convention the standard working week is Monday through Friday, and Saturday and Sunday are weekend days. The calculator walks the span day by day, counts the weekdays, then subtracts one for every holiday date that falls on a weekday inside the span. Holiday entries that land on a weekend, or outside the span, change nothing.

Business-day conventions are not universal: some countries use Sunday–Thursday work weeks, some have Saturday as a working day, and holiday calendars differ by country, state, and employer. That is why the holiday list is yours to fill in, and why the result is a planning number rather than a legal one.

Formula

Let S be the start date and E the end date, both inclusive:

$\text{calendar days} = E - S + 1$

$\text{business days} = \sum_{\substack{S \le d \le E \\ \text{weekday}(d)}} 1 \; - \; |\{\text{holidays in } [S,E] \text{ that are weekdays}\}|$

$\text{full weeks} = \left\lfloor \frac{\text{calendar days}}{7} \right\rfloor$

The holiday term counts each distinct holiday date once, even if it is entered twice, and only when it falls on a weekday within the span.

Worked example

Take the default span: August 3, 2026 (a Monday) through August 28, 2026 (a Friday).

The span contains four full Monday–Friday work weeks:

$4 \times 5 = 20 \text{ business days}$

Calendar days, counting both endpoints:

$28 - 3 + 1 = 26 \text{ calendar days}$

The difference is the six weekend days:

$26 - 20 = 6 \text{ weekend days}$

Full weeks are the 7-day blocks in the span:

$\left\lfloor \frac{26}{7} \right\rfloor = 3 \text{ full weeks, with 5 days left over}$

If you add August 10, 2026 (a Monday) as a holiday, the count drops by one:

$20 - 1 = 19 \text{ business days}$

The calendar days, weekends, and full weeks stay the same, because a holiday is still a calendar day.

Interpreting the result

A business-day count is a schedule assumption, not a guarantee. “Within 5 business days” means the 5th weekday after the reference point, but actual delivery depends on working hours, approvals, capacity, and local holidays that may not be on your list. Use the calendar-day and week columns to sanity-check the count: a span of 26 calendar days should always feel like about three and a half weeks.

For spans measured in hours rather than days, see the time duration calculator, which works with clock times. If you are converting a day count into weeks or months for planning, the days to weeks calculator and the day converter give those conversions with their own rounding conventions. And when the span is anchored to a birth date, the age calculator reports years, months, and days from that date instead of business days.

Tips

• Add holidays before comparing two scenarios. A single Monday holiday can turn a “10 business days” estimate into 11 calendar days.
• Double-check dates near year end: holiday calendars change yearly, and the December–January boundary mixes two holiday schedules.
• For “next business day after X” questions, set the end date one day after the due date you expect, or count by hand for a single day.
• If your organization counts a Saturday shift or a Friday–Saturday work week, this Monday–Friday tool is the wrong convention — adjust the inputs or count manually.

Common pitfalls

• Forgetting that the start and end dates are both included. A span from Monday to Friday shows 5 business days, not 4.
• Entering the same holiday twice; the calculator deduplicates, but the “holidays excluded” count then reflects one reduction, which is the correct behavior.
• Expecting a weekend holiday to shorten the count. It never does, because no weekday is removed.
• Comparing counts between tools that use exclusive endpoints or different holiday calendars without accounting for the convention difference.

Sources

• ISO, ISO 8601-1:2019 — Date and time — Representations for information interchange — calendar-week and date-representation conventions used for the weekday count.
• U.S. Office of Personnel Management, Federal holidays — example of an official holiday calendar that organizations commonly exclude from business-day counts.
• Wikipedia, ISO week date — description of the Monday-to-Sunday calendar week convention.