When planning delivery schedules, service level agreements (SLAs), or multi-phase construction timelines in Microsoft Excel, simply adding calendar days to a start date produces inaccurate forecasts because it fails to account for weekends and regional bank holidays. While Excel’s NETWORKDAYS function counts how many working days fall between two fixed dates, the WORKDAY and WORKDAY.INTL functions work in the opposite direction: they calculate the exact future or past completion date after a specified number of working days have elapsed.
In this guide, you will learn how to use the WORKDAY and WORKDAY.INTL functions in Microsoft Excel to calculate realistic project deadlines, define custom regional weekends, and exclude statutory public holidays from production schedules.
WORKDAY vs WORKDAY.INTL: What is the Difference?
Understanding which function suits your operational needs ensures your scheduling models remain flexible:
- WORKDAY: The classic function that assumes a standard Western Saturday-and-Sunday weekend. It accepts a start date, the number of working days, and an optional list of excluded holiday dates.
- WORKDAY.INTL: The international variant introduced to accommodate non-standard shift patterns, four-day working weeks, and countries where the official weekend falls on Friday and Saturday (such as in many Middle Eastern regions) or Sunday only.
How to Use the Standard WORKDAY Function
The syntax for the WORKDAY function is straightforward:
=WORKDAY(start_date, days, [holidays])Here is how each argument operates:
start_date: A valid Excel date representing the project launch date.days: The number of non-weekend, non-holiday working days required to complete the task. (Use a positive integer for future dates, or a negative integer to calculate backward deadlines).[holidays]: An optional cell range containing dates of public or company holidays to skip.
Practical Example:
Suppose a design project commences on Monday, 3 November 2025 (cell A2) and requires 15 working days. You also have a list of official bank holidays in cells F2:F5. Enter the following formula:
=WORKDAY(A2, 15, F2:F5)Excel evaluates 15 business days forward, automatically skips all intervening Saturdays and Sundays, skips any dates matching the holiday list in F2:F5, and returns the exact completion date.
How to Use WORKDAY.INTL for Custom Weekends
When your team operates on custom weekly rotas or regional work schedules, the WORKDAY.INTL function provides granular control over which days of the week are treated as non-working days:
=WORKDAY.INTL(start_date, days, [weekend], [holidays])The third argument, [weekend], allows you to define custom days off using either a numeric preset code or a 7-character binary string mask.
Option 1: Using Numerical Weekend Codes
| Code | Days Treated as Weekend |
|---|---|
1 (or omitted) |
Saturday, Sunday |
2 |
Sunday, Monday |
7 |
Friday, Saturday |
11 |
Sunday only |
17 |
Saturday only |
For example, to calculate a 10-day project in Dubai where the standard weekend is Friday and Saturday:
=WORKDAY.INTL(A2, 10, 7, F2:F5)Option 2: Using a 7-Character String Mask
For total flexibility across irregular shift rotas, you can provide a 7-character text string composed of 1s (non-working days) and 0s (working days), starting from Monday through to Sunday:
"0000011": Monday to Friday working; Saturday and Sunday off."0000111": Four-day week (Monday to Thursday working; Friday, Saturday, and Sunday off)."1010101": Alternate working days (Tuesday, Thursday, and Saturday active).
To schedule a 12-day task for a part-time employee working Monday through Thursday:
=WORKDAY.INTL(A2, 12, "0000111", F2:F5)Calculating Backward Kickoff Dates
If you have an immovable product launch date and need to know when preparation must commence, pass a negative number into the days parameter:
=WORKDAY(B2, -20, F2:F5)If cell B2 holds the hard delivery date of 18 December 2025, this formula counts backward 20 business days to reveal the exact kickoff date required to deliver on time.
Fixing the Five-Digit Serial Number Issue
If your formula returns a raw five-digit number like 45964 instead of a recognizable calendar date, do not worry. Excel internally tracks dates as serial integers starting from 1 January 1900. To display it properly:
- Select the calculated formula cell or column.
- Press Ctrl + 1 to open the Format Cells dialog.
- Under the Number tab, select Date.
- Choose your preferred regional date format (such as
DD/MM/YYYY) and click OK.
To broaden your date automation skills in spreadsheets, check out our guide on how to use the NETWORKDAYS.INTL function in Excel to calculate working days with custom weekends, or learn how to use the EDATE and EOMONTH functions in Microsoft Excel to calculate due dates and month ends.
Frequently Asked Questions
Does WORKDAY count the start date as day one?
No. By design, WORKDAY begins counting from the next business day after the specified start_date. If you set start_date as Monday and specify 1 day, the resulting date will be Tuesday.
Can I reference an empty holiday range?
Yes. If your project has no public holiday interruptions, you can omit the [holidays] argument entirely or reference an empty range; Excel will ignore holidays and filter weekends only.
What happens if the start date falls on a weekend?
Excel advances to the first subsequent valid business day before applying the requested day count, ensuring that weekend start times do not distort the elapsed work duration.