Working Day Calendars: Why a Holiday Looks Like Monday
When an automated working-day calendar marks a holiday as a Monday, it usually means the calendar is configured to treat the holiday as a non-working day and then shift the schedule to the next available working day, which can make the holiday itself appear on the Monday in the output. This article explains how working-day calendars work, why holidays can show up on Mondays, and how to fix or interpret such results.
What Is a Working-Day Calendar?
A working-day calendar (also called a business calendar) defines which days are available for work and which are not. It typically includes:
- Weekend days (usually Saturday and Sunday, but can vary by country or company).
- Public holidays (fixed dates like January 1, or floating ones like Easter Monday).
- Company-specific non-working days (e.g., a local fair day or a bridge day).
Automation systems—such as project management software, ERP systems, or scheduling tools—use this calendar to calculate deadlines, start dates, or durations while skipping non-working days. For example, if a task takes 3 working days and starts on Wednesday, the system will count Thursday and Friday, skip the weekend, and finish on the following Tuesday.
How a Holiday Can Appear as Monday
The confusion often arises when a holiday falls on a weekend. Many countries have a legal provision that if a public holiday lands on a Saturday or Sunday, the following Monday becomes a “substitute” or “in lieu” holiday. For instance, if January 1 is a Sunday, the Monday January 2 is a public holiday. Automation systems that implement this rule will mark that Monday as a non-working day. When you view the calendar, that Monday is shown as a holiday—even though the actual holiday date was Sunday.
Another scenario: some systems allow you to define holidays that are not tied to a specific date but to a day-of-week rule, like “the first Monday of September” (Labor Day in the US). In that case, the holiday is always on a Monday by definition.
Finally, if a holiday falls on a Tuesday or Thursday, many organizations observe a “bridge day” on the adjacent Monday or Friday to create a long weekend. If the system is configured to include such bridge days, it will mark that Monday as a non-working day, making it look like the holiday itself is on Monday.
How Automation Handles Holiday Shifts
When a holiday falls on a weekend, the automation has to decide whether to move the holiday to a weekday. The two common approaches are:
- No shift: The holiday is only on the actual date. If that date is a weekend, no extra day off is granted. The calendar simply shows the weekend as non-working.
- Shift to next working day: The holiday is moved to the next working day, which is usually the following Monday (if the weekend is Saturday-Sunday). This is the rule in many jurisdictions.
Systems that implement the shift will automatically mark the Monday as a holiday. The calculation of deadlines then skips that Monday as a non-working day.
Why Does This Cause Confusion?
People often look at a calendar and see a holiday label on a Monday, then wonder why the system is not working on that Monday. The confusion is usually because:
- The actual holiday date (e.g., Sunday) is not highlighted, but the substitute Monday is.
- The system may show the holiday name on the Monday, even though the official holiday is on the weekend.
- Different systems may handle the shift differently—some show the original date, some show the substitute, some show both.
For example, in the UK, if Christmas Day falls on a Saturday, the substitute holiday is the following Monday. A project management tool that is set to UK holidays will show Monday as a non-working day with the label “Christmas Day (substitute)”.
How to Choose the Right Working-Day Calendar
When setting up automation, you need to decide which holiday rule to follow:
- Check the legal holiday rules for the country or region where the work is performed. Many countries have official substitute holiday rules (e.g., EU countries, US federal holidays).
- Decide whether to include bridge days (e.g., if a holiday falls on Tuesday, do you also take Monday off?). This is usually a company policy, not a legal requirement.
- Select a calendar source that matches your needs: some systems offer built-in country calendars, others allow manual entry.
- Test with a known date (e.g., a holiday that falls on a weekend in the current year) to see how the system displays it.
Common Problems and How to Avoid Them
Here are typical issues users encounter with working-day calendars:
- Holiday on a weekend not shifted: The system may not automatically shift the holiday, so the Monday is a working day, but you expected it off. Solution: manually add the Monday as a holiday or change the calendar settings.
- Double-counting holidays: If you have both the original date and the substitute date marked as holidays, you lose an extra working day. Solution: check that the calendar only marks one day per holiday.
- Time zone differences: A holiday that starts at midnight in one time zone may appear on a different date in another. Solution: set the calendar to the time zone of the main office.
- Floating holidays: Some holidays are based on lunar calendars or religious observations that change each year. Solution: update the calendar annually or use a dynamic source.
Comparing Working-Day Calendars Across Systems
Different software handles holidays differently. For example:
- Microsoft Project uses a base calendar and allows you to mark holidays as non-working days. It does not automatically shift weekend holidays unless you manually set the substitute day.
- Google Calendar shows holidays from a public calendar, but it does not affect scheduling calculations unless you use a separate business calendar tool.
- Excel with WORKDAY function: The WORKDAY function in Excel skips weekends and any dates you list as holidays. If you include a weekend holiday in the list, it will skip it, but it will not automatically shift it to Monday. You must manually add the substitute Monday.
Therefore, the behavior you see depends entirely on how the system is configured.
Frequently Asked Questions
Why does my project management tool show a holiday on Monday when the actual holiday is on Sunday?
Because the tool is likely configured to shift weekend holidays to the next working day. This is a common legal rule in many countries. The tool marks Monday as a non-working day so that schedules do not assign work on that day.
How do I stop the system from shifting holidays to Monday?
Check the calendar settings. Look for an option like “Observe holidays on actual date only” or “Do not move holidays.” If no such option exists, you may need to manually edit the holiday list to remove the substitute day.
What is a “substitute holiday”?
A substitute holiday is a day off granted when a public holiday falls on a weekend. The day off is moved to a weekday, usually the following Monday, so workers still get the same number of days off. It is also called an “in lieu” holiday.
Does every country have substitute holidays?
No. Some countries, like the US, have federal substitute holidays for federal employees, but private employers may or may not observe them. Other countries, like Japan, do not have a general substitute holiday rule for all holidays (though some special rules exist). Always check the specific country’s labor law.
Why does Excel’s WORKDAY function not skip the Monday after a Sunday holiday?
Because Excel’s WORKDAY function only skips dates that you explicitly list as holidays. If you only list Sunday (the actual holiday) and that Sunday is a weekend, Excel already skips it as a weekend. It does not automatically add the Monday as a holiday. You need to add the Monday to the holiday list manually if you want it off.
Can I have a calendar that shows both the original holiday and the substitute day?
Yes, but that would result in two non-working days for one holiday. That may be acceptable if your company grants both days, but it will reduce the number of working days in the year. Most calendars show only one day per holiday.
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