WhenMathWhat "Holiday" Means in a Business-Day Calculation
A holiday calendar is a specific, dated list for a specific country and region, not a universal set of dates every calculation should assume.
Excluding "holidays" from a business-day count requires a specific, dated list, because holidays are not universal. They differ by country, sometimes by state or province within a country, and their calendar dates shift year to year even for a fixed-name holiday (Thanksgiving, Easter-linked holidays, and lunar-calendar holidays all move). A calculation that says "excluding holidays" without naming which country's list, and for which years, has not actually specified anything concrete yet.
Why the list has to be country- (and sometimes region-) specific
National holidays differ by country outright, but several countries also observe additional regional or state/province-specific holidays that a national-only list would miss, or observe a holiday on a different date depending on the region. A business-day calculation that assumes "the" holiday calendar without naming a specific country and, where relevant, a specific subdivision, is really assuming one particular list among several plausible ones.
Why the dates move even for a fixed-name holiday
Some holidays fall on a fixed calendar date every year (New Year's Day), but many are defined relative to a weekday-in-month rule (a specific Monday, the fourth Thursday of a month) or tied to a movable calendar such as a lunar or lunisolar calendar, meaning the actual date changes from year to year even though the holiday's name does not. A holiday-exclusion list has to be resolved for the specific year(s) a calculation spans, not memorized as a single fixed date.
How WhenMath keeps this current without a live network call
WhenMath ships a small, versioned static dataset of real public-holiday dates per supported country, generated at build time and covering a fixed multi-year range, rather than either hardcoding a single year's dates indefinitely or calling an external service at calculation time (which the site's browser-only, no-backend architecture rules out). Every business-day engine that excludes holidays states which country's list was applied directly in the result.
Key takeaway. A holiday exclusion is only meaningful once a specific country (and, where applicable, region) and year range are named. "Excluding holidays" alone is not yet a complete specification.
Frequently asked
- Which countries does WhenMath's holiday data cover?
- The current static dataset covers a defined set of countries generated at build time. Each holiday-aware engine's country selector shows exactly which lists are available, and the result states which one was applied.
- What happens for a country not in the dataset?
- A calculation without a matching holiday list falls back to excluding only weekends (or a custom workweek, if one is set), and the result states plainly that no holiday exclusion was applied, rather than silently guessing at a list.
- Do company-specific holidays (not public ones) work the same way?
- Company or team-specific non-working days are handled separately through the Custom Excluded-Date Calculator, which accepts a manually entered list rather than relying on any public holiday dataset.
Related engines
- Holiday Impact Calculator -- See how many working days a region's public holidays remove.
- Blackout-Date Deadline Planner -- Plan a business-day deadline around your own unavailable date blocks.
- Custom Excluded-Date Calculator -- Count business days after applying your own excluded dates.
- Business-Day Solver -- Solve for a start date, deadline, or business-day count, given the other two.
Last updated 2026-09-04