Business Days Calculator: How It Works

A business days calculator works out the number of working days between two dates, or the date that falls a set number of working days after a given start date. You enter a start date, an end date (or a count of days), and optionally a list of holidays, and it returns the total business days, excluding weekends and any holidays you specify. This is the tool businesses use to answer “how many working days until this order ships?” or “what date is 10 business days from today?”

Formula

The core calculation is straightforward: count the total calendar days between the two dates, then subtract the weekends. The standard formula for the number of business days between two dates (inclusive of both) is:

Business Days = Total Days − 2 × (Number of Full Weeks) − (Weekend Days in the Partial Week)

Where:

• Total Days = end date − start date + 1 (inclusive count)
• Number of Full Weeks = floor(Total Days / 7)
• Weekend Days in the Partial Week = the number of Saturdays and Sundays in the remaining days after removing full weeks

For adding business days to a date, the reverse is needed: convert business days to calendar days. A common approximation is to multiply the business days by 7/5 (since 5 business days = 7 calendar days on average) and add that to the start date, then adjust for the exact weekday. A more precise method uses a loop or a formula that accounts for the starting weekday.

Worked Example

Using the defaults from the calculator above: start date January 1, 2024 (a Monday), end date January 31, 2024 (a Wednesday).

1. Total calendar days = 31 − 1 + 1 = 31 days.
2. Number of full weeks = floor(31 / 7) = 4 weeks.
3. Weekend days in those full weeks = 4 × 2 = 8 days.
4. Remaining days after 4 weeks = 31 − (4 × 7) = 3 days (Monday, Tuesday, Wednesday). These are all weekdays, so 0 weekend days.
5. Total weekend days = 8 + 0 = 8.
6. Business days = 31 − 8 = 23 business days.

The calculator’s formula gives 23, matching the manual calculation.

For the second part: adding 10 business days to January 1, 2024. Using the approximation: 10 × 7/5 = 14 calendar days. January 1 + 14 days = January 15, 2024, which is a Monday. Since we started on a Monday and added 10 business days (exactly two weeks), the result is indeed January 15. The formula in the calculator gives the same date.

Why Business Days Matter

Business days are the default unit of time in most commercial and legal contexts. When a contract says “payment due within 10 business days,” it means 10 days excluding Saturdays, Sundays, and often public holidays. This matters because a week of business days is not the same as a calendar week: 5 business days is typically 7 calendar days, but if a holiday falls in between, it becomes 8 calendar days. Using a business day calculator avoids the common mistake of counting calendar days and underestimating deadlines.

Industries that rely heavily on business day calculations include:

• Banking and finance (settlement periods, loan approval times)
• Logistics and shipping (delivery estimates)
• Human resources (notice periods, leave accrual)
• Legal (filing deadlines, response times)
• Project management (task durations)

How to Use a Business Days Calculator

Most business day calculators ask for three pieces of information:

1. Start date – the day you begin counting.
2. End date – the day you stop counting (if calculating the number of days).
3. Number of days – if you want to find a future date instead.

Some calculators also let you specify a list of holidays. When you do, the calculator subtracts those dates from the total business days. For example, if you are calculating delivery days and the company is closed on a public holiday, that day should not count as a business day.

The result can be displayed in two ways: the total count of business days, or the actual date after adding a certain number of business days. Many calculators show both, as ours does.

Common Mistakes and Misconceptions

One frequent error is assuming that “business days” always means Monday through Friday. In some countries, the workweek is different (e.g., Sunday through Thursday in parts of the Middle East). Most calculators default to Monday–Friday, but you should check if your context uses a different definition.

Another mistake is forgetting to include the start date. If a task begins on Monday and takes 1 business day, it should be completed on Monday, not Tuesday. The inclusive vs. exclusive counting method must be consistent. Our calculator counts the start date as day 1.

A third misconception is that holidays are automatically included. They are not. Unless you explicitly add holidays, the calculator only excludes weekends. Always check the holiday list if your deadline involves a known public holiday.

Limitations of the Formula

The basic formula assumes a fixed 5-day workweek and no holidays. Real-world business calendars vary by country, region, and even company. For example, some companies observe additional holidays like the day after Thanksgiving in the U.S., which is not a federal holiday. The formula cannot know these company-specific days unless you input them.

Also, the formula does not account for half-days or reduced working hours. If a business closes early on Fridays, that is not reflected. For precise legal or contractual calculations, always verify with the specific terms of your agreement.

Alternatives to a Business Days Calculator

If you prefer not to use an online calculator, you can compute business days manually using a calendar. Count each day that is not a Saturday or Sunday, and skip any holidays you know about. This is feasible for short periods but becomes tedious for long ranges.

Spreadsheet software like Microsoft Excel or Google Sheets has built-in functions: NETWORKDAYS returns the number of business days between two dates, and WORKDAY returns a date after adding business days. Both accept an optional list of holidays. For example, in Excel: =NETWORKDAYS(A1, B1, holidays).

Programming languages also have date libraries that handle this. Python’s numpy.busday_count and JavaScript’s date-fns offer similar functionality. These are useful if you need to automate calculations in a larger workflow.

Frequently Asked Questions

Are Saturdays and Sundays always excluded?

In most of the world, yes, but not everywhere. Some countries have a workweek from Sunday to Thursday or Saturday to Wednesday. If you are working across borders, confirm the local workweek. Most calculators default to Monday–Friday, but you can often adjust the settings.

Do holidays count as business days?

No, unless you add them to the calculator. A holiday that falls on a weekday is not a business day. For instance, if July 4th is a Thursday, that day is not counted. You must manually enter holidays for the calculator to exclude them.

How many business days are in a year?

On average, there are about 260 business days in a year (52 weeks × 5 days). This varies slightly depending on the year and the number of holidays. In 2024, there are 262 business days in the U.S. (excluding federal holidays) because it is a leap year with 366 calendar days.

What does “within 5 business days” mean?

It means the task or response must be completed by the 5th business day after the starting point. If you start on Monday, the 5th business day is the following Monday (assuming no holidays). The count usually starts the next business day after the event, but always check the specific wording.

Can I use a business days calculator for past dates?

Yes. The calculator works the same for past dates. For example, you can find out how many business days ago an invoice was issued. Just enter the past date as the start and today’s date as the end.

Why does my calculator give a different result than Excel?

Because of differences in how the start and end dates are counted. Excel’s NETWORKDAYS includes both the start and end dates, while some calculators exclude the start date. Always check whether your calculator is inclusive or exclusive, and match it to your needs.

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in start | Start date | - | 2024-01-01 | 0
in end | End date | - | 2024-01-31 | 0
in days | Business days to add | - | 10 | 0
out bd_between | Business days between | days | max(0, floor((end - start) / 86400000) + 1 - 2 * floor((floor((end - start) / 86400000) + 1 + floor((start - 1) / 86400000) % 7) / 7)) | 0
out bd_after | Date after adding days | date | start + days * 7 / 5 * 86400000 | 0