Working days

Package: DATETIME_PACKAGE. Registered by createEngine(); for a slimmer engine, register it explicitly (see choosing packages).

A working day is a weekday, a day an office is open, so a deadline measured in working days skips the weekends in between. Solve counts them forward or back from a date, or across a window, and excludes public holidays too when the host supplies a calendar.

Deadlines count working days, not calendar days. Weekends are always skipped. An offset counts forward or back to a working day, and between counts the working days in a window, both ends included.

25/12/2023 + 5 workdays // Monday, January 1, 2024
working days between 01/01/2024 and 31/01/2024 // 23
workdays between 01/01/2024 and 31/01/2024 // 23
workdays in 3 weeks // 15

Counted from today, the answer moves with the day. The one shown is for noon on Wednesday 11 March 2026 in London, the fixed moment these pages are checked against, and the notepad gives yours.

3 business days from today // Monday, March 16, 2026

working and business days mean the same thing, and either reads in the singular for a count of one (1 working day after ...). workdays between, the unit’s own spelling, counts the same window, and how many may lead any of them.

10 business days after 2026-09-30 // Wednesday, October 14, 2026
10 working days before 2026-09-30 // Wednesday, September 16, 2026
1 working day from 2026-09-30 // Thursday, October 1, 2026
1 business day before 2026-09-30 // Tuesday, September 29, 2026
business days between 2026-09-01 and 2026-09-30 // 22
how many working days between 2026-09-01 and 2026-09-30 // 22

Every pairing reads the same way: working or business, in the singular or the plural, with after, from or before, and for the window workday between as well as the plural, each with or without how many in front.

10 working days after 2026-09-30 // Wednesday, October 14, 2026
10 business days before 2026-09-30 // Wednesday, September 16, 2026
1 business day after 2026-09-30 // Thursday, October 1, 2026
1 business day from 2026-09-30 // Thursday, October 1, 2026
1 working day before 2026-09-30 // Tuesday, September 29, 2026
workday between 2026-09-01 and 2026-09-30 // 22
how many business days between 2026-09-01 and 2026-09-30 // 22
how many workdays between 2026-09-01 and 2026-09-30 // 22

workdays until <date> and workdays since <date> are refused rather than answered, because the only reading they had was a fixed ratio of five working days to seven calendar days, which knows no weekends or holidays. Count from today with workdays between today and <date> instead.

Is a date a working day

A date can be asked whether it is a working day or falls on the weekend, which is how a note checks a deadline before it is agreed. is a workday, is a weekday and is a business day ask the first; is a weekend and is on a weekend ask the second. The answer is true or false.

2026-09-26 is a weekend // true
2026-09-26 is on a weekend // true
2026-09-26 is a business day // false
2026-09-28 is a workday // true
2026-09-28 is a weekday // true

The day of the week a date falls on, its month and its week number are on weekdays and week numbers.

A date in another zone

A date written in a zone (see time zones) is counted on that zone’s calendar, wherever the engine itself runs. Late on a Friday in New York is already Saturday in Europe, and a working day counted on the European calendar would land on a Sunday; counted on New York’s, it is the Monday, at the same time of day. working days between reads each zoned end as the day its own zone shows.

2024-11-01 23:30 in New York + 1 workday // Monday, November 4, 2024, 11:30:00 PM
2024-11-01 23:30 in Tokyo - 1 workday // Thursday, October 31, 2024, 11:30:00 PM
working days between (2024-11-01 23:30 in New York) and (2024-11-04 00:30 in Tokyo) // 2

The weekend and the holidays are the engine’s own (see below), read on the zone’s calendar: a holiday on 4 November moves that first line to the Tuesday.

Public holidays

Holidays cannot be worked out from a date the way a weekend can: they depend on the region and change year to year. So the engine excludes them only when the host application supplies a calendar, the same way it takes a data source for stocks or weather. Left unconfigured, working-day arithmetic skips weekends only, and says as much rather than guessing a holiday it was never told about.

A host passes the calendar as a list of dates or a predicate function:

new ExpressionEngine({
  config: { date: { holidays: ["2024-12-25", "2024-12-26"] } },
});
// or: { date: { holidays: (date) => isPublicHoliday(date) } }

With that calendar, 1 working day after 24/12/2024 steps over the 25th and 26th to the 27th, and working days between ... leaves them out of the count. The offset forms, between, and <date> + N workdays all consult it.

workdays in <span> and the is a workday / is a weekend questions stay weekends-only either way: the first has no date to look a holiday up on, and the second reports the shape of the week (is this a weekday), not whether a particular office is open.

Which days are the weekend

The weekend is Saturday and Sunday unless the host says otherwise. In much of the Middle East it is Friday and Saturday, so one working day after Thursday 1 January 2026 is Sunday 4 January, not Friday 2 January. A host sets the weekend by naming its days, and the first day of the week the same way:

createEngine({
  config: { date: { weekend: ["friday", "saturday"], firstDayOfWeek: "sunday" } },
});

With that engine, 1 working day after 2026-01-01 is Sunday, January 4, 2026, 2026-01-02 is a weekend is true, and start of week is the Sunday before. An empty list makes every day a working day. A name that is not a day of the week is refused when the engine is built, with DATE_WEEKDAY_INVALID, rather than quietly ignored.

Left unset, both come from the engine’s locale when its tag names a region and the runtime reports that region’s week (through Intl.Locale): ar-SA and he-IL have a Friday and Saturday weekend with the week starting on Sunday, en-US starts its week on Sunday, and en-GB on Monday. A bare language such as en, the default, names no region, so it keeps Saturday and Sunday and a Monday start. Each setting stands on its own: a host can name the weekend and let the locale choose the first day.

The weekend is what the working-day arithmetic skips, what is a weekend and is a workday answer from, and the first day is where the week forms on relative dates begin. Two things do not move with it: the ISO week number (week number of), which is Monday-based by definition, and workdays in <span> with the workday unit in a rate, which stay a fixed five working days to seven.