How every date is worked out

No date is typed into a page. Each one is produced by a function of the site's date engine, from a rule written in an Act, an order or a church calendar, and every page and tool calls the same functions. Automated tests compare the results with the official lists before each publication.

1. Bank holidays

For each of England and Wales, Scotland and Northern Ireland, the engine lists the days of Schedule 1 to the Banking and Financial Dealings Act 1971, the St Andrew's Day holiday of 2007 and the days appointed every year by proclamation under section 1: New Year's Day; 2 January in Scotland; St Patrick's Day in Northern Ireland; Good Friday; Easter Monday outside Scotland; the first and last Mondays of May; the Battle of the Boyne in Northern Ireland; the first Monday of August in Scotland and the last elsewhere; St Andrew's Day in Scotland; Christmas Day and Boxing Day.

Substitute days: a day that falls on a weekday stays. Then each day that falls on a Saturday or a Sunday moves, in calendar order, to the next weekday that is not already a bank holiday. This single rule reproduces every substitute day of the GOV.UK list, including Christmas on a Saturday (Monday 27 and Tuesday 28 December) and Scotland's 1 and 2 January at a weekend.

Official list first: for 2019 to 2028 the site shows the GOV.UK list itself, copied from its data feed on 28 October 2026. The tests check that the rule gives that list for all three jurisdictions and every year, except for days created or moved by special proclamation, which are named in the test file: 8 May 2020 (VE Day), 2 and 3 June 2022 (Platinum Jubilee), 19 September 2022 (state funeral), 8 May 2023 (coronation) and 15 June 2026 in Scotland (World Cup). After 2028, dates come from the rule and are labelled "expected" until a proclamation confirms them.

2. Working days

A working day is a Monday to Friday that is not a bank holiday of the nation you choose. Between two dates, both dates are counted. When adding working days, the start date is not counted. Local holidays (a council's own closure day, a school's training day) are not included.

3. The clocks

Since the Summer Time Order 2002, the Summer Time Act 1972 defines summer time as running from 1am GMT on the last Sunday in March to 1am GMT on the last Sunday in October, the period set by Directive 2000/84/EC. In local terms the clocks go from 1am to 2am in March, and from 2am back to 1am in October. The engine finds the last Sunday of each month and is tested against the GOV.UK table for 2025 to 2028.

4. Easter and the dates that hang on it

Easter Day is the first Sunday after the ecclesiastical full moon falling on or after 21 March, as set out in the Calendar (New Style) Act 1750. The engine uses the Meeus, Jones and Butcher algorithm, which reproduces the Gregorian tables, and is tested on known years and on the rule that Easter always falls between 22 March and 25 April. The Easter Act 1928, which would fix Easter, has never been brought into force. From Easter Day: Shrove Tuesday 47 days before, Ash Wednesday 46 days before, Mothering Sunday 21 days before (the Fourth Sunday of Lent in the Common Worship calendar), Palm Sunday 7 days before, Good Friday 2 days before, Easter Monday the day after.

5. Other dates

• Father's Day: third Sunday in June, a custom with no legal basis.
• Remembrance Sunday: second Sunday in November, the date of the National Service of Remembrance.
• Black Friday: the day after Thanksgiving in the United States, which falls on the fourth Thursday in November (OPM federal holidays); a retail custom, not a UK holiday.
• Bonfire Night, Burns Night, Halloween, saints' days: fixed dates, with the weekday computed.
• Ramadan and Eid al-Fitr: the Umm al-Qura calendar used in Saudi Arabia, as built into the international date libraries (ICU), copied into the site's data. Many UK mosques start a day later, after a local sighting of the crescent, so these dates are shown as expected, never as fixed.

6. Countdowns

The countdowns read your device clock after the page loads and count to midnight at the start of the date in your own time zone; for clock changes they count to the exact instant, 1am GMT. Before the page loads they show the day the site was built. Nothing is sent to us.

7. Updates

The script scripts/update-data.py downloads the GOV.UK bank holiday feed and stops with an error when it differs from the copy in the site, until a person has read the change. It is set to run every month once the site is online; until then, it is run by hand.

8. What the site does not do

• It does not say whether your employer, bank, school or shop is open.
• It does not include local or regional holidays outside the national lists.
• It does not keep anything you enter.

Method version of 28 October 2026. A date that looks wrong: contact.