Public Holidays: How It Works
Public holiday dates are less fixed than they appear. Some move with the moon, some with the ecclesiastical calendar, some shift to the nearest Monday, and some are declared with only weeks of notice — which is why holiday calendars are a recurring source of scheduling error.
Four kinds of holiday
| Type | Behaviour | Examples |
|---|---|---|
| Fixed date | Same date every year | New Year's Day, Christmas, national days |
| Fixed weekday | Nth weekday of a month | US Thanksgiving, UK bank holidays |
| Lunar or ecclesiastical | Moves each year | Easter, Eid, Diwali, Chinese New Year |
| Declared | Announced by government | State funerals, coronations, elections |
The last category is the one that breaks systems. A one-off holiday announced six weeks ahead will not be in any calendar dataset compiled earlier, and it can invalidate a delivery estimate, a payroll run, or a legal deadline calculated on business days.
Moving holidays
Easter falls on the first Sunday after the first full moon on or after the spring equinox — a formula that shifts it across five weeks and drags Good Friday and Easter Monday with it. Orthodox Easter uses the Julian calendar and usually falls on a different date entirely.
Islamic holidays follow a purely lunar calendar of about 354 days, so they move roughly eleven days earlier each Gregorian year and cycle through the seasons. Many are confirmed only on local moon sighting, which means the date can differ between countries and can be finalised only a day in advance.
Hindu, Chinese, Jewish and Buddhist observances use lunisolar calendars with intercalary months, so they move within a range but do not drift indefinitely.
Substitute days
Many countries shift a holiday falling at a weekend to the nearest working day — commonly the following Monday. Practice varies: some move only Sunday holidays, some move both, and some do not move any. This is a frequent source of confusion for anyone counting business days across a border.
Regional variation
Within a single country, holidays commonly differ by state, province or region. India's holiday calendar varies substantially between states, the UK has different bank holidays in Scotland and Northern Ireland, and Germany's differ by Land. A national list is often an incomplete description of what any particular office actually observes.
Bank holidays, public holidays and school holidays are also distinct categories that only partly overlap — a day that closes schools may not close offices.
Practical guidance
- For a deadline that matters, check the holiday calendar of the specific jurisdiction, not the country.
- Confirm moving holidays for the actual year rather than assuming last year's date.
- Add a buffer around lunar holidays, whose exact date may not be fixed until close to the day.
- Watch for declared holidays, which appear at short notice.
- For cross-border work, check both calendars — one side's working day is regularly the other's holiday.
Holiday data varies by source and is subject to late change. Confirm against an official government calendar for anything with legal or financial consequences.