How to Calculate Business Days Between Two Dates

What Counts as a Business Day?

A business day (also called a working day) is any day on which the standard commercial economy operates. In most jurisdictions that means Monday through Friday, excluding public holidays. Saturdays, Sundays, and recognised holidays are excluded. The definition matters because contracts, payroll, court filings, and shipping deadlines almost always count business days rather than calendar days.

The international standard ISO 8601 numbers Monday as day 1 and Sunday as day 7 — a useful convention when implementing the math in code, because integer division by 7 cleanly separates weekday counts from full weeks.

The Core Weekday Formula

The standard approach for counting business days between a start date and an end date (inclusive of both) is:

1. Compute the total number of calendar days between the two dates.
2. Compute the number of full 7-day weeks in that span — each contributes exactly 5 business days.
3. Add the weekday count of the partial week at the end (0 to 5 days).
4. Subtract any public holidays that fall on a Mon–Fri inside the range.

Algebraically, if D is the total day count and w is the weekday of the start date (Mon = 0, Sun = 6):

full_weeks = ⌊D / 7⌋
business_days = full_weeks × 5 + adjustment(w, D mod 7) − holiday_count

Worked Example: 1 March to 31 March 2025

March 1, 2025 is a Saturday; March 31 is a Monday. The calendar span is 31 days. There are 4 full weeks (28 days), contributing 20 weekdays, plus a partial 3-day tail (Sat, Sun, Mon) contributing 1 weekday. That gives 21 business days. If the country observes a public holiday on a weekday in March (the US does not in 2025; India observes Holi on March 14), subtract one for each.

The Working Days Calculator does this arithmetic instantly, but the manual method is worth knowing because it surfaces the off-by-one issues described below.

Country-by-Country Differences

The "Mon–Fri minus holidays" rule is nearly universal in the West, but the holidays themselves vary widely:

If your calculation crosses borders — for example, an international contract with a US vendor and an Indian buyer — both holiday calendars matter. The conservative rule is to count a day as non-business if either jurisdiction treats it as a holiday.

Holiday Adjustment Rules

Most countries shift holidays that fall on a weekend to the nearest weekday. In the US, a holiday falling on Saturday is observed on the preceding Friday; one falling on Sunday is observed on the following Monday. The UK uses similar "substitute days" for bank holidays. Japan is an exception: Saturday holidays are simply lost. When you write a business-day calculator, the holiday list must contain the observed date, not the nominal one.

Floating versus Fixed Holidays

Some holidays sit on the same date every year (Christmas Day = December 25). Others float to a fixed weekday in a fixed week — US Thanksgiving is the fourth Thursday of November; UK Spring Bank Holiday is the last Monday of May. Lunar holidays (Eid, Diwali, Chinese New Year) require an entirely separate calendar engine.

Common Mistakes

• Off-by-one (inclusive vs exclusive endpoints). "From Monday to Friday" can mean 4 days (exclusive of one end) or 5 days (inclusive of both). Pick a convention and document it. Most contracts mean inclusive.
• Forgetting the start day's weekday. Five 7-day weeks always contain 25 weekdays — but a span of "5 weeks starting on a Saturday" contains 25 weekdays only if you start counting from the next Monday.
• Treating half-days as full days. Christmas Eve and New Year's Eve are half-days in many European countries. They are not public holidays in law, so a strict business-day count includes them, but many companies treat them as non-working internally.
• Ignoring observed dates. If Independence Day (4 July) falls on a Sunday, the federal observance is Monday 5 July — and that Monday is the non-business day, not Sunday.
• Mixing up weekend conventions. The Gulf states historically observed Thursday–Friday weekends. Most have shifted, but legacy contracts may still use the old definition.

A Quick Sanity Check

For any whole number of weeks, the business-day count must be exactly 5 times the number of weeks (before holiday subtraction). 52 weeks contain 260 weekdays. A non-leap year of 365 days has either 260 or 261 weekdays, depending on whether the year starts on a Saturday or Sunday. A leap year (366 days) has 260, 261, or 262 weekdays. If your calculator returns a number outside that band for a full year, something is wrong.

Try the Working Days Calculator →