Business Days Calculator: How It Works

This calculator works out the number of business days between two dates, or the date that falls a given number of working days after a start date. You enter a start date, an end date (or a count of days), and optionally a list of holidays, and you get the exact number of Monday–Friday days in that range. The result excludes weekends and any holidays you add, so you can plan delivery times, payment terms, or project deadlines with confidence.

Formula

The core formula counts the total days between the two dates, subtracts weekends, and then subtracts any holidays that fall on weekdays. In symbols:

Business days = (Total days) − (Weekend days) − (Weekday holidays)

Where:

• Total days = end date − start date + 1 (inclusive of both dates)
• Weekend days = 2 × (number of full weeks) + (extra weekend days from the remainder)
• Weekday holidays = number of holidays that fall on Monday–Friday within the range

All dates are treated as calendar dates, and the result is an integer. If the end date is before the start date, the result is 0 (not negative).

Worked Example

Using the default values: start = 2024-01-01, end = 2024-01-31, holidays = 2024-01-15 (Martin Luther King Jr. Day in the US).

1. Total days = 31 − 1 + 1 = 31 days.
2. Number of full weeks = floor(31 / 7) = 4 weeks, remainder = 3 days.
3. Weekend days = 4 weeks × 2 = 8 weekend days, plus the remainder days (Jan 29, 30, 31) which are Mon, Tue, Wed – no weekends, so 0 extra. Weekend days = 8.
4. Weekday holidays = Jan 15 is a Monday, so 1.
5. Business days = 31 − 8 − 1 = 22.

The calculator gives 22, matching the manual count.

Why Use Business Days Instead of Calendar Days?

Business days reflect when companies, banks, and government offices actually operate. A contract that says “delivery in 5 business days� means about a week of calendar time, but if a holiday falls in that week, it extends. Using calendar days can mislead you by a day or two, which matters for deadlines, payment terms, and shipping estimates. Business days are the standard for:

• Invoice payment terms (e.g., “net 30â€� usually means 30 calendar days, but “5 business daysâ€� means working days)
• Shipping and delivery promises
• Legal and regulatory filing windows
• Project management timelines

How to Use the Calculator

Enter a start date and an end date to get the count of business days between them, inclusive. If you want to know the date after a certain number of business days, you can set the end date far ahead and adjust, but this calculator is designed for counting between two dates. Add holidays in the text box, one per line, in YYYY-MM-DD format. The calculator automatically ignores any holiday that falls on a weekend, because those days are already excluded.

For example, if you start on a Friday and count 2 business days, the result is the following Tuesday (skipping Saturday and Sunday). If you add a Monday holiday, it becomes Wednesday.

Common Mistakes and Limitations

The most common error is forgetting that the count is inclusive of both start and end dates. A task from Monday to Friday is 5 business days, not 4. Another mistake is entering holidays that fall on weekends – they don’t reduce the count because they’re already excluded. Also, this calculator assumes a standard Monday–Friday workweek. It does not account for:

• Half-days or partial working days
• Regional holidays that are not in your list
• Weekends that are not Saturday–Sunday (e.g., in some countries the weekend is Friday–Saturday)
• Floating holidays that change each year (you must add them manually)

For most business purposes, the standard workweek is sufficient, but if you operate in a country with a different weekend, you’ll need a custom calculator.

How to Choose a Business Days Calculator

When selecting a business days calculator, look for these features:

• Ability to add custom holidays (most important)
• Inclusive counting option (start and end both counted)
• Option to exclude weekends automatically
• Clear display of the formula or method used
• Support for date formats you use (e.g., YYYY-MM-DD vs MM/DD/YYYY)

Some calculators also let you set a custom workweek (e.g., Monday–Saturday). This is useful for industries like retail or logistics that operate six days a week.

Frequently Asked Questions

How do I count business days including today?

If you start today and want to count 3 business days, set the start date to today and the end date to today plus 3 days, then adjust the end date until the result shows 3. The calculator counts inclusively, so today counts as day 1. For example, if today is Wednesday, 3 business days from today (including today) is Friday.

What if a holiday falls on a weekend?

If a holiday falls on Saturday or Sunday, it does not reduce the business day count because those days are already excluded. The calculator automatically ignores weekend holidays. You only need to add holidays that fall on Monday–Friday.

Are Saturdays ever considered business days?

In most office environments, no. But in retail, hospitality, and some manufacturing, Saturday is a working day. This calculator assumes a standard Monday–Friday workweek. If you need to include Saturdays, look for a calculator that lets you customize the workweek.

How do I calculate business days between two dates in Excel?

Excel has a built-in function called NETWORKDAYS. You write =NETWORKDAYS(start_date, end_date, [holidays]). The holidays argument is optional and can be a range of cells containing dates. Excel automatically excludes weekends (Saturday and Sunday) and any holidays you list. This calculator does the same thing without needing a spreadsheet.

What is the difference between business days and working days?

They are essentially the same. Both refer to days when most businesses operate, typically Monday through Friday, excluding public holidays. Some people use “working days� to include Saturdays in certain industries, but the common definition is identical.

Related

• Is Overtime Calculated Daily or Weekly?
• Global Dates Calculator: How to Compare Dates Worldwide
• Gap Between Dates Calculator: How It Works

in start | Start date | - | 2024-01-01 | 0
in end | End date | - | 2024-01-31 | 0
in holidays | Holidays (one per line, YYYY-MM-DD) | - | 2024-01-15 | 0
out business_days | Business days | days | max(0, floor((end - start) / 86400000) + 1 - floor((end - start) / 86400000) / 7 * 2 - holidays_count) | 0